1. Field of the Invention

The present invention relates to a process for stabilizing unmilled brown rice or partially milled brown rice using ethanol or ethanol vapors, and stabilized unmilled brown rice (and brown rice flours produced therefrom) produced by the aforementioned process.

2. Background and Summary of the Invention Brown rice has the potential for being a nutri¬ tionally valuable food source. The bran layers of the brown rice kernel are rich in dietary fiber, minerals, oil, and vitamins, particularly the B vitamins. The results of recent studies indicate that these bran layers may also have cholesterol-reducing properties (Kahlon et al., "Influence of rice, oat and wheat bran...", Abstract FASEB, March 1989; and M. Hegsted et al., "Stabilized Rice Bran and Oat Bran Lower Cholesterol in Humans", abstract FASEB Journal 1990, Vol. 4, page A368) . Marketing of the kernels, flours, bran and oil of brown rice, however, has been limited due to the suscepti¬ bility of the oil in the bran to readily becoming rancid leading to off-odors, off-flavors, and shortened shelf life. A large percentage of rice exported by the U.S. is shipped as brown rice, since other countries find it more economical to mill it themselves. At the elevated temper¬ atures experienced during transport, the oil in unstabi- lized brown rice is subject to lipolysis. Bran high in free fatty acids (FFA) loses its animal feed and food value. The higher the FFA in the oil, the more uneconomi¬ cal it is to refine. The losses for potentially edii-Je oil during refining are two to three times the FFA content of the oil (Enochian et al., 1981, "Stabilization of rice bran with extruder cookers..." A preliminary analysis of operational and financial feasibility, U.S. Department of Agriculture Marketing Res. Report 1120) .

Brown rice lipids are subject to both oxidative and enzymatic deterioration. Brown rice lipids are

readily hydrolyzed by Upases, both natural to the bran and of microbial origin that release free fatty acids. Free fatty acids are the precursors of the above-mentioned off flavors and off odors which are associated with lipid degradation products generated in subsequent oxidation reactions. Oxidative deterioration can be slowed by using optimum packaging materials, temperatures, and atmospheres for storage (Mitsuda et al. , "Underwater and Underground Storage of Cereal Grain", Food Tech. 26:50-56, 1972: Saubhagya, 1976, "Lipid autooxidation in rice", J. Food Sci. 41:1018-1023: Ory et al. , 1980, "Storage quality of brown rice as affected by packaging..." J. Food Protection 43:929-932: Sharp et al. , 1986, "Effects of storage time..." Cereal Chem. 63:247-251. Two approaches have been taken to stabilize brown rice to enzymatic hydrolysis by lipase: 1) inactivating lipase by subjecting raw or brown rice to moist or dry heat (U.S.P. 2,585,978 to Van Atta et al. , 1952: U.S.P. 2,992,921 to Bardet et al., 1961; U.S.P. 4,582,713 to Hirokawa et al., 1986) or to parboiling or precooking processes (U.S.P. 3,086,867 to Miller, 1963; U.S.P. 3,959,515 to McCabe, 1976; Sowbhagya, 1976, supra) ; and 2) removing kernel oil which serves as a substrate for lipase by organic solvent extraction (U.S.P. 2,538,007 to Kester, 1951; U.S.P. 3,261,690 to Wayne, 1966 (as dis¬ cussed more fully in "Solvent Extractive Rice Milling" in Rice Chemistry and Technology. D.F. Houston, Editor, Am. Assoc. of Cereal Chemists, St. Paul, Minnesota)). The aforementioned Kester patent teaches stabilizing brown rice using room temperature petroleum ether or boiling hexane as extractive solvents.

Stabilization of brown rice in accordance with the present invention has advantages over hexane extraction, as taught by Kester (U.S.P. 2,538,007). Such advantages include 1) flour stable to free fatty acid (FFA) formation cannot be produced from brown rice kernels extracted with 68°C hexane; 2) ethanol is more effective than hexane in extracting free fatty acids from rancid brown rice; 3)

ethanol is a GRAS (generally recognized as safe) solvent and residual amounts remaining in the extracted rice will not affect the suitability of the product for human consumption; and 4) ethanol is a less volatile, safer solvent. The aforementioned Wayne patent is drawn to providing an improved milling process, including milling in the presence of an extractive solvent. By contrast the present invention does not contemplate milling and thus retains the bran on the rice kernel; i.e. the instant invention produces a stabilized full-fat brown rice or partially defatted (10-15% oil removal) brown rice, and flours of the foregoing.

"Effects of Solvent Extraction by Immersion on the Quality and Storage Stability of Rice" by Cheigh et al. in Korean J. Food Sci. Technol. Vol. 4, No. 4 (1972), p. 271- 275; and "On the Oxidation of Rice Lipid Fractions Ex¬ tracted from the Whole Grain by Immersion" by Cheigh et al. in Korean J. Food Sci. Technol. Vol. 4, No. 3 (1972), p. 206-212; both apparently (English language translations are not available) disclose extraction of polished white rice with ethanol. By contrast, while the instant inven¬ tion employs ethanol extraction, it does not involve mechanical milling for bran removal, extracts a minimal amount of oil, and results in stabilized brown rice kernels which can be ground to form stabilized brown rice flour.

The present invention is drawn to a highly advan¬ tageous and unobvious process for stabilizing unmilled brown rice comprising contacting unmilled brown rice with ethanol (i.e. this term encompasses pure 100% absolute ethanol as well as aqueous mixtures including ethanol) under conditions providing extraction of 15% or less of brown rice oil (as well as otn&r components of the rice) from the unmilled brown rice by said ethanol in order to produce stabilized unmilled brown rice and ethanol having rice extracts therein, without milling of the rice during the contacting, and separating the stabilized unmilled brown rice from the ethanol having rice extracts therein.

Alternatively, the process comprises contacting unmilled or partially milled brown rice with ethanol vapor

(i.e. the phrase "ethanol vapor" encompasses either vapor of pure 100% absolute ethanol, or vapor of aqueous ix- tures including ethanol) under conditions providing no substantial loss of oil from the unmilled or partially milled brown rice by the ethanol vapor, thereby producing stabilized unmilled or partially milled brown rice and ethanol having rice extracts therein; and separating the stabilized unmilled or partially milled brown rice from the ethanol having rice extracts therein.

Other aspects of the present invention include production by the aforementioned processes, of stabilized unmilled brown rice or partially milled brown rice and stabilized unmilled brown rice or partially milled brown rice flour having highly advantageous and unobvious properties. As for example, not being susceptible to enzymatic deterioration by lipase, having improved storage stability, absence of solvent(s) not generally regarded as safe, having very low bacterial and fungal populations, desirable kernel surface appearance, highly desirable cooking properties, and minimal loss of minerals, thia- ine, protein, dietary fiber and carbohydrates, etc. BRIEF DISCUSSION OF THE DRAWINGS Figure 1 is a graph of % free fatty acid by weight of lipid in solvent-extracted and control brown rice kernels versus months stored at 36°C.

Figure 2a is a graph of % free fatty acid by weight of lipid in flours prepared from solvent-extracted and from control brown rice kernels versus months stored at room temperature (approximately 25°C) .

Figure 2b is a graph of % free fatty acid by weight of lipid in flours prepared from solvent-extracted and from control brown rice kernels versus months stored at 36°C.

Figure 3a is a graph of the change in conjugated diene hydroperoxides "ΔCDHP" (micromoles per gram of rice, dry basis) in solvent-extracted and in control brown rice

kernels versus months stored at room temperature (approxi¬ mately 25°C) .

Figure 3b is a graph of ΔCDHP (micromoles per gram of rice, dry basis) in solvent-extracted and control brown rice kernels versus months stored at 36°C.

Figure 4a is a graph of ΔCDHP (micromoles per gram of rice, dry basis) in flours prepared from solvent- extracted and control brown rice kernels versus months stored at room temperature (approximately 25°C) . Figure 4b is a graph of ΔCDHP (micromoles per gram of rice, dry basis) in flours prepared from solvent- extracted and control brown rice kernels versus months stored at 36°C.

Figure 5 is a side view of an apparatus which was employed for treating brown rice kernels with ethanol vapors. (A) 500 ml round bottom two neck glass flask; (B) heating mantle; (C) glass vent tube; (D) 3 cm X 12 cm glass butt tube holding 40g brown rice; (E) wire mesh sample retaining screen; (F) plexiglass jacket; (G) inlet; and (H) outlet for jacket water.

Figure 6 is a graph of % free fatty acids by weight of lipid in brown rice kernels treated with vapors from boiling aqueous ethanol for 3, 5, and 10 minutes, control kernels, and heat-treated kernels versus months stored at 36°C.

Figure 7 is a graph of % free fatty acids by weight of lipid in flours prepared from brown rice kernels treated with vapors from boiling aqueous ethanol for 3, 5, and 10 minutes, control kernels, and heat-treated kernels versus months stored at 36°C.

Figure 8 is a graph of change in conjugated diene hydroperoxides content "ΔCDHP" (micromoles per gram of rice, dry basis) in brown rice kernels treated with vapors from boiling aqueous ethanol for 3, 5, and 10 minutes, control kernels, and heat-treated kernels versus months stored at 36°C.

Figure 9 is a graph of change in conjugated diene hydroperoxides content "ΔCDHP" (micromoles per gram of

rice, dry basis) in flours prepared from brown rice kernels treated with vapors from boiling aqueous ethanol for 3, 5, and 10 minutes, control kernels, and heat- treated kernels versus months stored at 36°C. DESCRIPTION OF PREFERRED EMBODIMENTS

The term ethanol is utilized in the accompanying specification and claims. In its well established art accepted meaning (see e.g. The Condensed Chemical Dictio¬ nary, 10th ed. , G. Hawley, ed. , 1981, page 423) it is defined to include either (1) pure 100% absolute ethanol (dehydrated) ; or (2) aqueous mixtures including ethanol. such as food (U.S.P.) grade which consists essentially of about 95% by volume ethanol and about 5% by volume water. The contacting employed in the present invention may include either continuous or batch contacting of the ethanol with the unmilled brown rice. In continuous contacting, the unmilled brown rice may be moved in counter current to flow of the ethanol (e.g. either fresh- pure ethanol or ethanol containing rice extracts recycled from a previous extraction) . Alternatively, the contact- - ing may be carried out in several batch steps. Either by contacting a single batch of unmilled brown rice with several portions of fresh ethanol, or by sequentially contacting a single portion of ethanol with several batches of unstabilized unmilled brown rice. The afore¬ mentioned process of batch extraction using several portions of fresh ethanol has the advantage of minimizing the amount of residual rice oil deposited on the surface of the stabilized rice following separating; i.e. when the ethanol having rice extracts therein is separated from the stabilized brown rice some of the rice oil remains on the surface of the rice. With each subsequent extraction with fresh ethanol, the rice oil concentration in the ethanol is lower. As the rice oil concentration in the ethanol is reduced, less rice oil is deposited on the surface of the rice. While a relatively large amount of rice oil on the surface of the rice is not a problem if the rice is to be packaged so as to exclude oxygen from the stabilized

unmilled brown rice, it is desirable to produce stabilized unmilled brown rice having a low surface oil content if the rice is to be stored or packaged so as to be exposed to oxygen. The aforementioned process of batch extraction using sequential contacting of a single portion of ethanol with several batches of unstabilized unmilled brown rice has the advantages of: (1) producing a rice which retains its full oil content, and (2) utilizing the ethanol to its greatest extractive capacity. The contacting of the present invention, whether for production of stabilized unmilled brown rice or flour, may be carried out at any of a wide range of temperatures. For example, the contacting may be carried out at tempera¬ tures from about 0°C to about 78°C, as for example, at about room temperature i.e. from about 10°C to about 35°C when heating or cooling of the rice and ethanol is not desired or is considered uneconomical. For production of stabilized flour, it is preferred to utilize a temperature range of from about 55°C to about 78°C. Use of this elevated temperature (l) facilitates penetration of the ethanol into the rice thus facilitating denaturing and thus deactivation of lipase in the rice; (2) the heat itself may have a role in denaturing and deactivation of the lipase, and (3) provides greater removal of free fatty acids, which is of particular advantage in treatment of rancid unmilled brown rice.

The present invention permits either treatment of freshly dehulled unmilled brown rice, which typically has a free fatty acid content of less than 4% by weight of lipid (i.e. the free fatty acid (FFA) content is less than 4% by weight of the total lipid content of the rice) to produce a stable product, or treatment of brown rice which has become rancid (e.g. during storage or shipping) . Such rancid unmilled brown rice typically has a free fatty acid content of 4% or more by weight of lipid. Brown rice oil is readily hydrolyzed by the action of lipases, both natural to the bran and of microbial origin that release free fatty acids. Accumulation of free fatty acids

- 8 - imparts to the rice organoleptically unacceptable off- flavors and sour odors. Contacting of rancid unmilled brown rice with ethanol in accordance with the present invention extracts free fatty acids (FFA) therefrom, thus restoring the rice to a low FFA content. Extracting of rancid unmilled brown rice with ethanol at 78°C may remove up to about 77% of the FFA present.

The instant invention also encompasses a step of separating the rice extracts from the ethanol having rice extracts therein, so that the ethanol may be reused for further extraction. The rice extracts may be separated from the ethanol using conventional separations such as distillation, adsorption, ion exchange or membrane separa¬ tion. In a continuous process employing such separation and ethanol recycling, ethanol will need to be added to the process because a small amount of ethanol will leave the process as residue on the rice. In accordance with the present invention, the stabilized unmilled brown rice may have a residual ethanol content of up to about 1,000 parts per million by weight.

Separation of the stabilized unmilled brown rice from the ethanol may be carried out in any convenient manner. For example the ethanol having rice extracts therein may be drained from the stabilized brown rice and any residual ethanol having rice extracts therein remain¬ ing on said rice may be evaporated therefrom. Evaporation may be promoted by use of elevated temperature, reduced pressure, etc. Subsequent to said separation, the rice may be ground, using standard grinding techniques to produce a stabilized brown rice flour. It is also contem¬ plated that the flour could be supplemented with desirable materials (e.g. Thiamine) obtained from the ethanol used for extraction. Brown rice stabilized in accordance with the present invention, by extraction at 78°C, would provide a product which can be milled to yield partially defatted, food quality stabilized bran. The full-fat bran obtained from room temperature (RT) ethanol (EtOH) extrac¬ tion may require further processing to eliminate residual

lipase activity. Both EtOH-extracted brown rice products would be suitable for obtaining oil low in FFA.

In an alternate embodiment, the contacting em¬ ployed in the present invention may include either contin- uous or batch contacting of ethanol vapor with unmilled or with partially milled brown rice. In continuous contact¬ ing, the unmilled or partially milled brown rice may be moved through conventional equipment either counter- current, co-current, or cross-current to the flow of ethanol vapor. In batch contacting, either fresh-pure ethanol vapor or ethanol vapor from previous treatments (i.e. ethanol vapor is contacted with a first batch of unmilled or partially milled brown rice, separated there¬ from, and subsequently contacted with at least one addi- tional batch of unmilled or partially milled brown rice) may be used.

It is preferred that the contacting with ethanol vapors be carried out at temperatures at or above the condensation point of ethanol vapor (78° for 95% v/v ethanol at atmospheric pressure) . A preferred temperature range for carrying out the contacting at atmospheric pressure or above is from about 78°C to about 100°C depending upon the concentration of ethanol used (100% to 1%, v/v) . Pressure and temperature ranges used vary directly with ethanol concentration used and the accompa¬ nying condensation temperature of its vapors. Super¬ heated ethanol vapor may be used but may result in starch gelatinization. A variety of pressures may be utilized in practicing the instant application (i.e. below atmospheric pressure) at atmospheric pressure, or above atmospheric pressure. When subatmospheric pressure (i.e. pressure below atmospheric) is utilized, the preferred temperature range is from about 15°C to about 100°C. It is preferred to carry out the contacting of rice and ethanol vapor in an atmosphere which is saturated with ethanol vapor, in order to promote thorough contacting of the rice with the vapor.

Typically unmilled brown rice has about 12-13% moisture (moisture that rough rice is typically dried to after harvest) . Rice having such typical moisture content or drier rice may be vapor-treated in accordance with the present invention. Prior to ethanol vapor treatment, it is preferred to l) reduce the moisture (i.e. water con¬ tent) of the rice to a level where it is essentially in equilibrium with the water content of the ethanol vapor (i.e. this step may be utilized so that the ethanol vapor will not absorb water from the rice and the rice will not absorb water from the ethanol vapor) and 2) raise and maintain the temperature of the kernels at or above the condensation temperature of the ethanol vapor. This will prevent condensation of ethanol on the kernels, and no moisture, oil or bran components will be lost. Condensa¬ tion of ethanol on the kernels is not desirable since a small amount of kernel oil (<3%) and possibly some other bran components will be extracted. Also a water content equilibrium between the ethanol vapor and the rice may be achieved by prior to the step of contacting, measuring the water content of the rice and selecting and utilizing in said step of contacting, ethanol vapor having a water content which is essentially in equilibrium with the measured water content of the rice. Anhydrous ethanol vapors are not preferred since they will readily absorb water from the rice kernels and condense.

When the contacting is carried out using operating conditions under which the ethanol does not condense (or appreciably condense) , the separating of rice and ethanol will involve separating rice from ethanol which consists of vapor, or consists essentially of vapor. When the contacting is carried out using operating conditions under which the ethanol partially condenses, the separating of rice and ethanol will involve, separating the stabilized rice from condensed ethanol which may contain rice ex¬ tracts (some oil and other bran components) and from ethanol vapor and evaporating condensed residual liquid ethanol from the stabilized rice.

Subsequent to the separation, rice stabilized in accordance with the present invention may be ground to flour using conventional grinding equipment and methods. The present invention also encompasses such a step of grinding unmilled or partially milled brown rice which has been stabilized in accordance with the instant invention, as well as flour produced thereby.

The instant invention also encompasses a step of separating the rice extracts from the ethanol having rice extracts therein, so that the ethanol may be reused for further extraction. The rice extracts may be separated from the ethanol using conventional separations such as distillation, filtration, centrifugation, adsorption, ion exchange or membrane separation. In a continuous process employing such separation and ethanol recycle, ethanol will need to be added to the process because a small amount of ethanol will leave the process as residue on the rice. In accordance with the present invention the stabilized unmilled brown rice may have a residual ethanol content of up to about 200 parts per million by weight.

The present invention produces stabilized unmilled or partially milled brown rice, not susceptible to enzy¬ matic deterioration by lipase, not having gelatinized starch and having essentially full oil content, produced by the processes as described hereinabove. It is pre¬ ferred that the contacting provides extraction of about 5% or less of brown rice oil from the unmilled or partially milled brown rice so as to retain its full nutritional value. The following examples are intended only to further illustrate the invention and are not intended to limit the scope of the invention -*:; defined by the claims.

Example . Rough rice samples of Tebonnet (1988 crop) were obtained from the Louisiana State University Rice Experi¬ ment Station, Crowley, LA. The samples were dehulled in a McGill Sheller (H. T. McGill, Houston, TX) .

A 500g sample of freshly dehulled brown rice was placed in a jacketed, stainless steel, cylindrical (6" diameter x 6" deep) extractor which was fitted with a 12 mesh stainless steel sample retaining screen in the bottom.

Extractions were performed at either room tempera¬ ture or at 78°C. Hot water (78°C) was circulated through the extractor jacket for extractions performed at 78°C. The first extraction was made with 800g of aqueous ethanol (95%, v/v) . The solvent was circulated at a flow rate of 1 L/min. for 20 min. after which the solvent was drained. Two additional 20 min. extractions were performed using 600g of solvent for each. The solvent-extracted rice kernels were desolventized in air overnight or in air followed by vacuum (10mm, 35°C, 1 hr.). Brown rice flours were prepared by grinding extracted kernels to a powder in a Udy Cyclone Mill (Udy Corp., Fort Collins, CO) using a 40 mesh sieve screen.

Unextracted brown rice kernels and flours prepared from these served as controls. Brown rice kernels were placed in a 78°C oven for 1 hour to allow the effect of heat on kernel stability to be evaluated. To compare the action of aqueous ethanol with that of the common, commer¬ cial vegetable oil extractive solvent hexane, brown rice kernels were extracted with Getty-B hexane at 68°C for 4 hours using a soxhlet. The kernels were desolventized overnight in air. Flours were prepared by grinding the hexane-extracted kernels.

Brown rice kernel and flour samples were stored in pint-size capped glass jars at room temperature or 36°C with no humidity control. Two batches of ethanol-extract¬ ed, hexane-extracted, and control brown rice kernel and flour samples were subjected to analytical tests to determine compositions, bacterial and mold populations, and storage stabilities.

Total dietary fiber, protein, moisture, ash, fat, and thiamine contents of the solvent-extracted and control rice samples were determined in duplicate by the American

Assoc. of Cereal Chem., 1983, Approved Methods of the AACC, the Assoc, St. Paul, MN; and the Association of Official Am. Chem, 1990, Official Methods of Analysis, 15 ed. The Assoc. Arlington, VA. Elemental compositions were determined in duplicate on HNO ₃ -HC10 ₄ (3:1) digests of ground rice samples utilizing inductively coupled plasma spectroscopy (ICP) .

For microbiological assays, 10-g samples of rice were weighed, transferred aseptically into sterile blender jars and blended with 90 ml of sterile pH 7.2 phosphate- buffered distilled water. Serial dilutions of 10 ^"1 , 10 ^"2 , and 10 ^"3 were prepared using sterile pH 7.2 phosphate- buffered distilled water. Duplicate nutrient agar pour plates for total plate counts and triplicate potato dextrose agar plates for total molds were inoculated with the appropriate dilutions and incubated as described by DeLucca et al., 1978, "Isolation and identification of lipolytic microorganisms found on rough rice from two growing areas", J. Food Protection 41:28-30. As a measure of the extent of lipolytic hydrolysis of brown rice kernels and flours during storage, the free fatty acids contents of solvent-extracted and control rice samples were determined the day following solvent extrac¬ tion and then periodically by a micro method, Hoffpauir et al., 1947, "Germination and free fatty acids...", Science

106:344-345. Meta-cresol purple was substituted for the phenolphthalein indicator. Free fatty acids content was calculated as oleic acid and expressed as percent of oil.

As a measure of oxidative deterioration of unsatu- rated lipids in brown rice kernels and flours during storage, ΔCDHP content was determined by the method of St. Angelo et al., 1972, "A comparison of minor constituents in peanut butter as possibly sources...", J. Am. Peanut Res, and Educ. Assoc. 4:186-197. Samples were ground in a Udy cyclone mill (Udy Corp., Boulder, CO) to pass through a 40-mesh screen. Duplicate one gram samples were ex¬ tracted with 25 milliliters (ml) high performance liquid chromatography grade hexane for 30 min. Absorbency at

234.0 n was determined, using hexane as a reference. An A _s of 24,500 mol liter ^-1 cm ^"1 was used to calculate the concentration of CDHP in micromoles per gram brown rice (dry basis) . A Hitachi S-510 scanning electron microscope was used to examine the surfaces of the solvent-extracted and control kernels. The rice grains were attached to aluminum sample stubs with double adhesive tabs. No fixation and dehydration processes were necessary. Prepared stubs were sputter-coated with gold/palladium to prevent charging in the electron beam. The stubs were observed at 10 kV accelerating voltage.

Table I compares the compositions of room tempera¬ ture (RT) and 78°C ethanol (EtOH)-extracted brown rice kernels to those of unextracted (control) and 68°C hexane- extracted brown rice kernels.

TABLE I

Compositions of untreated (control), RT EtOH-extracted, 78°C EtOH- extracted, and 68°C hexane-extracted Tebonnet (long grain) brown

Values given are on a dry basis and are means for duplicate analyses with the following S. E. M. : moisture +.0.1%, nitrogen + 0.1%, TDF + 0.3%, ash + 0.03%, thiamine + 0.1%, minerals + 1%, and free fatty acids + 0.05%. Values given for fat analyses are means of ten determinations with S. E. M. < 0.1%. Free fatty acids are expressed as percentage of total oil content of sample.

- 16 -

Less than 3% of the oil was removed from brown rice kernels which were extracted with ethanol (EtOH) at room temperature (RT) . Extraction of brown rice with EtOH at 78°C or hexane at 68°C removed approximately 15% of the kernel oil. Ninety-five percent of the brown rice thia¬ mine was retained in the RT EtOH-extracted kernels. However, extraction of brown rice kernels with EtOH at 78°C reduced their thiamine content 68%. Eighteen percent of the kernel thiamine was lost using 68°C hexane as the extraction solvent. No loss of protein (nitrogen) , total dietary fiber, or carbohydrate and minimal loss of miner¬ als occurred when brown rice was extracted with EtOH or hexane.

Extraction of freshly dehulled brown rice kernels with 78°C EtOH yielded a product with a free fatty acid (FFA) content approximately 50% that of unextracted kernels. The brown rice products resulting from RT EtOH or 68°C hexane extractions had FFA contents approximately 85% that of the control. Likewise, a reduction in FFA contents was observed when brown rice kernels with high FFA contents were solvent-extracted. Extraction of brown rice kernels with a FFA content of 27% with 78°C EtOH led to a 77% decrease in FFA content. Room temperature EtOH and 68°C hexane extractions of this rice led to 33% and 57% reductions in FFA, respectively.

The residual ethanol contents of air-desolventized 78°C and RT EtOH-extracted brown rice kernels were approx¬ imately 830 ppm and 115 ppm, respectively. After desolventizing by vacuum, residual EtOH contents were approximately 260 ppm and 50 ppm, respectively, for 78°C and RT EtOH-extracted kernels.

Visually no differences could be seen between the RT EtOH-extracted kernels and control kernels. Kernels extracted with 68°C hexane were slightly dull in appear- ance. The 78°C EtOH-extracted kernels appeared duller and drier. Scanning electron micrographs (SEM) revealed the extent of disruption of the caryopsis coat (peicarp, testa, nucellus) caused by solvent extraction. The

undulating caryopsis coat of the control brown rice kernels appeared more wavy at 2OX magnification following solvent extraction. Magnification at 2000X revealed narrow crease marks on the surfaces of the RT EtOH- and 68°C hexane-extracted kernels, which were not present on the surfaces of the 78°C EtOH-extracted kernels, giving the surface a hill and valley appearance.

Table II shows the bacterial and mold populations of solvent-extracted and control brown rice kernels and their flours, initially and after 5 months of storage at RT.

TABLE II

Microbial populations of solvent-extracted and control brown rice kernels and their flours, initially and after 5 months of storage at RT. Kernels (k), Four (f)

TREATMENT TOTAL PLATE COUNT MOLD COUNT

(No./g) (No./g)

Initial 5 Months Initial 5 months

Total plate counts decreased during storage. Total plate counts were very low in the solvent-extracted kernels and flours prepared from these kernels. The mold counts of the brown rice kernels and flours were low. No countable mold was observed in the 78°C EtOH-extracted kernels and flours prepared from same.

FFA levels in solvent-extracted brown rice kernels which were air- or vacuum-desolventized did not change during 6 months of storage at RT, while that of control kernels increased from 4% to 6%. At a storage temperature of 36°C, the FFA levels in RT EtOH- and 68°C hexane- extracted kernels increased from 3.3% to 4.3%; the FFA level in the 78°C EtOH-extracted kernels remained at 1.8%. When stored at 36°C for 6 months, the FFA level of the

control kernels increased from 4% to 9.8%. There were no differences in the FFA levels during storage of control kernels and those of kernels which were heated at 78°C for 1 hour prior to storage. Figure 1 shows the effect of storage time at 36°C on FFA levels in solvent-extracted and control born rice kernels.

Figures 2a and 2b show the effect of storage time at RT and 36°C, respectively, on FFA levels in flours prepared from control and solvent-extracted brown rice kernels which were air-desolventized. FFA levels in¬ creased rapidly in control flour samples which were stored at RT or 36°C. The rate of increase in FFA levels was greater at the elevated storage temperature. FFA levels also increased rapidly in flour samples prepared from RT EtOH- and 68°C hexane-extracted brown rice kernels stored at RT or 36°C, but at lower rates than the control flours. There were only slight increases in FFA levels in flour prepared from 78°C EtOH-extracted brown rice which were stored at RT or 36°C. Decreasing the residual EtOH content of this flour by vacuum-desolventizing to the amount found in the flour prepared from RT EtOH-extracted kernels (approximately 100 ppm) did not change the rate of FFA formation. During storage there were no differences in the FFA contents of the control flour and that of flour prepared from brown rice kernels which were heated in an oven at 78°C for 1 hour.

Figures 3a and 3b depict the change in development of conjugated diene hydroperoxides (ΔCDHP) in solvent- extracted and control brown rice kernels during storage at room temperature and 36°C, respectively. Initial CDHP levels in the 78°C EtOH- and 68°C hexane-extracted kernels were lower than those in RT EtOH-extracted and control kernels. The hot solvents appear to have extracted CDHP. CDHP levels in the 78°C EtOH-extracted kernels increased rapidly during storage at RT or 36°C. In contrast, CDHP levels in RT EtOH-extracted, 68°C hexane-extracted, and control kernels only gradually increased during storage at RT or 36°C. In flours prepared from solvent-extracted and

control kernels, CDHP levels increased rapidly during the first 3 months of storage and then leveled-off, as shown in Figures 4a and 4b. After 3 months of storage at RT, CDHP levels were approximately the same in the flours prepared from control and EtOH-extracted kernels was slightly lower. After 3 months of storage at 36°C, CDHP levels in flours prepared from RT EtOH-extracted, 68°C hexane-extracted, and control kernels were approximately the same; the CDHP level in the flour from 78°C EtOH- extracted kernels was higher.

Extraction of brown rice with aqueous ethanol (95%, v/v) at room temperature yielded a full-fat product with a free fatty acid content approximately that of freshly dehulled rice. A product with approximately a 15% lower oil content and a free fatty acid content approxi¬ mately half that of freshly dehulled rice resulted from extraction of brown rice with EtOH at 78°C.

Thiamine was chosen as an indicator of the degree of retention of the B vitamins, which can be extracted from rice bran by ethanol (Talwalkar et al., 1965, "Rice bran - a source material for pharmaceuticals", J. Food Sci. , Technol. 2:117-119). Thiamine retention was 95% and 32% in the RT and 78°C EtOH-extracted kernels, respective¬ ly. In comparison, thiamine retention was 82% in the 68°C hexane-extracted kernels. The 78°C EtOH apparently pene¬ trated the kernel layers to a greater extent than the RT EtOH or 68°C hexane solvents, thus leaching more thiamine. There was no or minimal loss of protein, dietary fiber, carbohydrates, and minerals in the EtOH- or hexane-ex- tracted brown rice kernels.

Aqueous ethanol and hexane extractions of brown rice decreased the bacterial population of the rice to very low levels. Total plate counts decreased during storage, as was observed previously during the storage of brown rice (Ory et al. , 1980, supra) .

Brown rice has a short shelf life (approximately 3-6 months) because of enzymatic and oxidative deteriora¬ tion of bran lipids. Brown rice oil is readily hydrolyzed

by the action of lipases, both natural to the bran and of microbial origin, that release free fatty acids (DeLucca et al., 1978, supra) . Accumulation of FFA imparts to the rice organoleptically unacceptable off-flavors and sour odors. Hydroperoxides are the primary products of the reaction of oxygen with unsaturated lipids (Frankel, 1961, Hydroperoxides, p. 51 in: Sym. on Foods: Lipids and their Oxidation, H.W. Schultz ed., The Avi Pub. Co., Inc., Westport, CT) . These degrade to form volatile carbonyl compounds, which impart off-flavors and rancid off-odors to brown rice (Frankel, 1961, supra, Sharp et al., 1986, supra) .

Aqueous ethanol and hexane extractions stabilized brown rice kernels to lipolytic hydrolysis, as indicated by no increase or a minimal increase in FFA in the ex¬ tracted kernels. The action of aqueous ethanol in stabi¬ lizing brown rice can be attributed to ethanol 1) denatur¬ ing bran lipases and thus deactivating them and 2) reduc¬ ing bacterial and mold populations by killing the organ- isms. DeLucca et al. (1978, supra) determined that approximately 10% of the total bacterial population on rough rice and all of the isolated molds showed lipolytic action. A third action of ethanol, which also explains the action of hexane, is the removal of kernel oil which serves as a substrate for lipase. Within the intact rice kernel, lipases are localized in the testa-cross layer region of the caryopsis coat, while the oil is localized in the aleurone and germ (Shastry et al., 1971, "Studies on rice bran lipase", Ind. J. Biochem. Biophys. 8:327- 332) . Damage to kernels during shelling disrupts these regions allowing oil and lipase to mingle and lipolysis to proceed. Solvent extraction of this "freed" oil removes the substrate from the lipase. Kester et al. supra, found that the oil which is removed from whole brown rice kernels with fat solvents had the characteristics of being unstable in the grain (in contact with lipase) and stable when extracted from the grain (enzyme absent) .

Flour prepared from 78°C EtOH-extracted kernels was stable to lipolysis, whereas flours prepared from control, RT EtOH-extracted, and 68°C hexane-extracted kernels were not stable. The large increases in FFA in flour samples prepared from RT EtOH-extracted and 68°C hexane-extracted kernels can be explained by these sol¬ vents not penetrating the kernel surface sufficiently to deactivate all of the lipase. Grinding these kernels to flours allows the oil and lipase to make contact and lipolysis to occur. In contrast, 78°C EtOH apparently penetrated further into the bran layers and deactivated all of the lipase. SEM micrographs revealed that 78°C EtOH was more effective in penetrating the coat and deactivating the kernel lipase. The large increases in FFA in the flours prepared from control, RT EtOH-extracted, and 68°C hexane-extracted kernels can not be attributed to differences in the lipolytic bacterial and mold populations of the flour and kernel samples, since no significant differences in microbial populations were observed between these samples. The stability of the flour prepared from 78°C EtOH- extracted kernels to lipolysis was not due to the higher residual level of EtOH in the flour or the higher tempera¬ ture of extraction, as supported by our experimental results.

Conjugated diene hydroperoxides (CDHP) levels increased rapidly in the 78°C EtOH-extracted brown rice kernels, indicating susceptibility of these kernels to oxidative rancidity. Only slight increase in CDHP levels were observed in the control, RT EtOH-extracted, and 68°C hexane-extracted kernels. Since the 78°C EtOH disturbed the caryopsis coat to a greater extent than the other solvents, it left the kernel lipids more susceptible to oxidative deterioration. An economically feasible, stable, full-fat product can be produced by extracting brown rice with aqueous ethanol at room temperature. Aqueous ethanol extraction of brown rice at 78°C produces a partially defatted

product which is stable to lipolysis. This product, however, would be more susceptible to oxidative deteriora¬ tion than unstabilized brown rice. With proper packaging oxidative deterioration of brown rice can be slowed (Ory et al., 1980, supra. Sharp et al. , 1986, supra) and thus it should not be a deterrent to extracting rice with 78°C EtOH. Thiamine retention in 78°C EtOH-extracted brown rice is poor, but the thiamine could be recovered from the ethanol and added to the rice or flour. Extraction with 78°C EtOH would be the preferred method for obtaining a product suitable for making brown rice flour which is stable to lipolysis or for extracting rice high in FFA and restoring it to a product with a low FFA content.

Example 2 Rough rice samples of Tebonnet (1989 crop) were obtained from the Louisiana State University Rice Experi¬ ment Station, Crowley, Louisiana. The samples were dehulled in a McGill Sheller (H. T. McGill, Houston, Texas) . Figure 5 depicts the apparatus employed for treating brown rice samples with vapors from boiling ethanol. A 40 gram (g) sample of freshly dehulled brown rice was placed in a jacketed (F) , glass butt tube (3 cm dia. x 12 cm high) (D) which was fitted with a wire mesh sample retaining screen (E) . Water from a water bath set at 83°C was circulated through the jacket (F) . After the temperature of the sample reached 78°C, which required 20 minutes, the glass butt tube (D) was inserted into the neck of a 500 ml round bottom flask (A) containing boiling aqueous ethanol (95% v/v; b.p. 78°C) . Samples were treated with ethanol (EtOH) vapors for 3, 5 and 10 min¬ utes. Following treatment the samples were transferred to shallow stainless steel pins and allowed to cool in room temperature (24°C) air. Brown rice samples at 12.8% moisture (moisture level of control) and 8.0% moisture were treated with EtOH vapors. Samples at 8.0% moisture were obtained by drying the 12.8% moisture brown rice for 2.5 hours at 65°C.

Untreated brown rice kernels and flours prepared from them served as controls. Brown rice kernels were placed in a 83°C jacketed, glass butt tube for 30 minutes to allow the effect of heat on kernel stability to be evaluated. To compare the action of aqueous EtOH with that of the common, commercial vegetable oil extractive solvent hexane, brown rice kernels were treated with vapors from boiling hexane (b.p. 68°C) .

Brown rice flours were prepared by grinding vapor- treated kernels to a powder in a Udy Cyclone Mill (Udy, Corp., Fort Collins, Colorado) using a 20 mesh sieve screen. Brown rice kernel and flour samples were stored in half pint-size capped glass jars with air headspace at 36°C. Two batches of vapor-treated and control kernel and flour samples were subjected to analytical tests to determine thiamine content, bacterial and mold popula¬ tions, and storage stabilities.

As a measure of the extent of lipolytic hydrolysis of brown rice kernel and flour lipids during storage, the free fatty acids contents of vapor-treated and control rice samples were determined the day following vapor treatment and then periodically by a micro method, Hoffpauir et al., 1947, "Germination and free fatty ac¬ ids...", Science 106:344-345. Meta-cresol purple was substituted for the phenolphthalein indicator. Free fatty acids content was calculated as oleic acid and expressed as percent of oil.

As a measure of oxidative deterioration of unsatu- rated lipids in brown rice kernels and flours during storage, conjugated diene hydroperoxides "CDHP" content was determined by the method of St. Angelo et al., 1972, "A comparison of minor constituents in peanut butter as possible sources...", J. Am. Peanut Res, and Educ. Assoc. 4:186-197. Samples were ground in a Udy cyclone mill (Udy Corp., Boulder, Colorado) to pass through a 20-mesh screen. One-half gram samples were shaken with 25 ml high performance liquid chromatography grade hexane for 30 minutes and then filtered through 0.45 μm Millex-HV

Millipore filters. Absorbencies of the filtrates at 234.0 nm were determined, using hexane as a reference. An absorptivity coefficient (A _s ) of 24,500 mol liter ^-1 cm ^-1 was used to calculate the concentration of CDHP in micro - oles per gram brown rice (Dry basis) .

For microbiological assays, lOg samples of rice water weighed, transferred aseptically into sterile blender jars and blended with 90 ml of sterile pH 7.2 phosphate-buffered distilled water. Serial dilutions of 10 ^-1 , 10 ^"2 , and 10 ^-3 were prepared using sterile pH 7.2 phosphate-buffered distilled water. Duplicate nutrient agar pour plates for total plate counts and triplicate potato dextrose agar plates for total molds were inoculat¬ ed with the appropriate dilutions and incubated as de- scribed by DeLucca et al., 1978, "Isolation and identifi¬ cation of lipolytic microorganisms found on rough rice from two growing areas", J. Food Protection 41:28-30.

Thiamine contents of vapor-treated and control rice samples were determined in duplicate by the Associa- tion of Official Analytical Chemists, 1985, Official Methods of Analysis, 14th ed. , The Association, Arlington, VA.

Free fatty acids (FFA) were determined periodical¬ ly during storage as a measure of the extent of lipolytic hydrolysis of lipids in brown rice kernel and flour samples. Figure 6 shows the effect of storage time at 36°C on the accumulation of FFA in brown rice kernels (12.8% moisture) which were treated with vapors from boiling aqueous EtOH, heat-treated, or untreated (con- trol) . Samples were stored at 36°C to accelerate the rate of lipolytic hydrolysis. FFA levels in brown rice kernels treated with EtOH vapors for 3 or 5 minutes increased from 3.0% to 3.9% and 3.6%, respectively, after 6 months of storage at 36°C. There was no change in FFA content in kernels treated with vapors for 10 minutes, while that of control kernels increased from 3% to 24%. During storage the increase in FFA in heat-treated kernels was approxi-

mately 15% lower than that of the control kernels, indi¬ cating some deactivation of lipase by heat-denaturation.

The vapors from boiling aqueous EtOH extracted surface water from the kernels and condensed on the kernels during treatment. The vapor treatment lowered the moisture content of the brown rice kernels approximately 1.5%; loss of kernel oil was less than 3%. To determine whether the action of the EtOH vapors in stabilizing brown rice kernels to FFA formation depended on the vapors condensing on the kernels, brown rice kernels at 8.0% moisture were treated with EtOH vapors. The EtOH vapors did not condense on the 8% moisture kernels; the water content of the kernels did not change and no oil or other bran components were extracted. FFA levels did not increase in the 10 minute vapor-treated 8% moisture kernels following storage at 36°C. Thus, vapors from boiling aqueous EtOH were effective in stabilizing the kernels to FFA formation. Stabilization was not dependent on the vapors condensing into a liquid. Figure 7 shows the effect of storage time at 36°C on FFA levels in flours prepared from 12.8% moisture brown rice kernels treated with EtOH vapors. Following 5 months of storage, FFA levels in flours prepared from kernels treated with vapors for 3, 5, and 10 minutes increased from 3% to 9%, 7%, and 6%, respectively. In contrast, the FFA levels in flours prepared from control and heat- treated kernels increased from 3% to 80% and 46%, respec¬ tively. The low increased in FFA in the flours prepared from 3, 5, and 10 minutes vapor-treated kernels indicated a low level of residual lipase activity in the flours.

Vapors from boiling hexane were ineffective in preventing FFA formation in brown rice kernels. Following one month storage at 36°C, the FFA level in kernels treated with hexane vapors for 3, 5, and 10 minutes increased from 3% to 18%, 17%, and 12%, respectively; the FFA levels in control kernel and heat-treated kernels increased to 17% and 14%, respectively.

Conjugated diene hydroperoxide (CDHP) contents were determined periodically during storage as a measure of the extent of oxidative deterioration of unsaturated lipids in brown rice kernel and flour samples. Figures 8 and 9 depict the effects of storage at 36°C on the devel¬ opment of CDHP in brown rice kernels treated with EtOH vapors and flours prepared from these kernels, respective¬ ly. CDHP levels increased rapidly in the kernels treated with EtOH vapors and in their flours. Only a slight increase in CDHP level was observed for control and heat- treated kernels during storage. The higher rate of increase in CDHP in the EtOH vapor-treated kernels and their flours compared to the control kernels and flour, indicates an increased susceptibility of the lipids in the former to oxidative rancidity.

Table III shows the effect of EtOH vapor treatment on the bacterial and mold populations of brown rice kernels. Total plate counts and mold counts were very low in the EtOH vapor-treated kernels. The vapors from boiling aqueous EtOH denatured the organisms and thus killed them.

TABLE III

Effect of EtOH vapor treatment on microbial population of brown rice. Counts were determined one week after dehull- ing kernels. Initial moisture content 12.8%.

TREATMENT Control

Heat-Treated

3 minutes EtOH Vapors

5 minutes EtOH Vapors

10 minutes EtOH Vapors

Brown rice is rich in the B vitamins. Thiamine was chosen as an indicator of the degree of retention of the B vitamins in kernels treated with EtOH vapors. As shown in Table IV, there was no loss of thiamine in the EtOH vapor-treated kernels.

TABLE IV

Effect of EtOH vapor treatment on thiamine content of brown rice.

TREATMENT THIAMINE

(mg/lOOg)

12.8% MOISTURE BROWN RICE Control 0.72

Heat-Treated 0.74

3 minutes EtOH Vapors 0.72

5 minutes EtOH Vapors 0.72

10 minutes EtOH Vapors 0.73 8.0% MOISTURE BROWN RICE

Control 0.72

Heat-Treated 0.71

10 minutes EtOH Vapors 0.71

An economically feasible, stable, full fat, product with ungelatinized starch can be produced by treating brown rice with the vapors from boiling aqueous EtOH. Brown rice kernels stabilized by EtOH vapor treat¬ ment are stable to lipolytic hydrolysis, as indicated by no or minimal increases in FFA during storage. EtOH vapors act by denaturing lipases endogenous to the brown rice kernel with concomitant deactivation. The longer the treatment time, the more effective the EtOH vapors were in denaturing the endogenous lipases. Since endogenous lipases are so close to the kernel surface, denaturation by ethanol vapors is plausible. The action of EtOH vapors can also be attributed to ethanolic denaturation of bacteria an mold found on the kernel surfaces, which kills the organisms. DeLucca et al., 1978, supra, determined that approximately 10% of the total bacterial population on rough rice and all of the isolated molds showed lipo¬ lytic action. Microbial and mold lipases are possibly more contributory to free fatty acid formation in brown rice than endogenous lipases (DeLucca and Ory, 1987, "Effects of microflora on the quality of stored rice", Trop. Sci. 27:205-214). Loeb and Mayne, 1952, "Effect of

moisture on the microflora and formation of free fatty acids in rice bran", Cereal Chem. 29:163-175, found a relationship between moisture content of rice, microflora, and free fatty acids formation in rice bran. Brown rice kernels stabilized to lipolytic hydro¬ lysis by EtOH vapors were more susceptible to oxidative deterioration than untreated kernels. However, with proper packaging, oxidative deterioration of brown rice can be slowed (Ory et al., 1980, "Storage quality of brown rice as affected by packaging..." J. Food Protection 43:929-932; Sharp and Timme, 1986, "Effects of storage time..." Cereal Chem. 63:247-25) and thus it should not be a deterrent to utilizing this process.