BACKGROUND

PRIORITY CLAIMS

This application claims priority from NIPO application No. 21631, filed 24 February. 2021, the contents of which are incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present invention relates to the field of food products, more specifically, the present invention relates to improving a shelf life of a food product using a coconut paring residue extract (CPRE).

DESCRIPTION OF RELATED ART

The “background” description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present invention.

Food products deteriorate during storage and transportation, and while cooking. To reduce deterioration, food preservatives such as antioxidants are often added to the food products. Due to health concerns associated with synthetic antioxidants, there is high interest in the use of natural antioxidants as food preservatives. Conventionally used natural antioxidants such as, vitamins, tocopherols, carotenoids, and phenolic compounds, although capable of reducing oxidative damage and extending a shelf life of a food product, often suffer from drawbacks like poor thermal stability. For example, it has been reported that processing pineapple into jam destroyed nearly 50% of the vitamin C content. Although, use of natural antioxidants, such as a vitamin E, can be used to improve the shelf life of bakery products, a considerable amount of the vitamin E is lost during baking. It was reported that the vitamin E content in milled barley decreased by 8% at 120 °C within 24 hours.

Yet another drawback associated with the conventionally used natural antioxidants as food preservatives is their impact on a sensory quality. Certain plant extracts add flavors to food products but are not suitable as preservatives. For instance, extracts from plants such as garcinia, curcumin, vanillin, and mint have been reported to have limited uses in bakery products.

Each of the aforementioned methods suffers from one or more drawbacks hindering their adoption. Accordingly, there exists a need to develop methods of improving the shelf life of the food products using food preservatives that are safe for human consumption, and that can withstand high temperatures, without compromising on the sensory quality of the food.

SUMMARY

In one aspect of the present disclosure, a method of improving a shelf-life of a food product is described. The method includes adding to the food product a food preservative consisting of a coconut paring residue extract (CPRE) having 2-4 weight/volume (w/v) % phenolic compounds.

The foregoing general description of the illustrative embodiments and the following detailed description thereof are merely exemplary aspects of the teachings of this disclosure and are not restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of this disclosure and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

FIG. 1 A to FIG. 1C is a statistical representation of antioxidant activities of a coconut paring residue extract (CPRE) and synthetic antioxidants, butylated hydroxytoluene (BHT) and butylated hydroxyanisole (BHA), by various antioxidant assays, according to one embodiment of the present disclosure;

FIG. 2 depicts a thermal stability of the CPRE, according to one embodiment of the present disclosure;

FIG. 3 A depicts prepared cooked pork samples for a thiobarbituric acid reactive substances (TBARS) assay, according to one embodiment of the present disclosure;

FIG. 3B depicts formation of TBARS as a malondialdehyde per kg meat with time in cooked pork samples, according to one embodiment of the present disclosure; FIG. 4 depicts preservation of egg-based food products by the CPRE, according to one embodiment of the present disclosure;

FIG. 5 is a graphical representation of inhibition of a b-carotene bleaching with time in a fruit juice and a vegetable juice by the antioxidants (CPRE, BHT, and a control), according to one embodiment of the present disclosure;

FIG. 6 depicts the effect of the antioxidants (CPRE, BHT, and the control) on a peroxide value in baked vanilla cakes, according to one embodiment of the present disclosure;

FIG. 7 depicts the effect of antioxidants (CPRE, BHT, and the control) using a hexanal as an index of a lipid oxidation, in the baked vanilla cakes, according to one embodiment of the present disclosure;

FIG. 8 is a graph comparing the effect of the antioxidants (CPRE, BHT, and the control) on physical parameters in cakes, according to one embodiment of the present disclosure;

FIG. 9 is a graph comparing the effect of the antioxidants (CPRE, BHT, and the control) on a sensory quality in cakes, over a period, according to one embodiment of the present disclosure; and

FIG. 10 depicts a microbial shelf life of the antioxidant added cakes, according to one embodiment of the present disclosure.

DETAILED DESCRIPTION

Reference will now be made in detail to specific embodiments or features, examples of which are illustrated in the accompanying drawings. Wherever possible, corresponding or similar reference numbers will be used throughout the drawings to refer to the same or corresponding parts. Moreover, references to various elements described herein, are made collectively or individually when there may be more than one element of the same type. However, such references are merely exemplary in nature. It may be noted that any reference to elements in the singular may also be construed to relate to the plural and vice-versa without limiting the scope of the disclosure to the exact number or type of such elements unless set forth explicitly in the appended claim.

The terminologies and/or phrases used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as is commonly understood by one of ordinary skill in the art. For clarity, the following specific terms have the specified meanings. Other terms are defined in other sections herein.

As used herein, the term “shelf life” refers to the length of time for which a food product can be stored before it goes bad or becomes unsafe to eat.

As used herein, the term, “oxidation of food” refers to a chain reaction that occurs in the presence of oxygen, responsible for the deterioration in the quality of food products, including off-flavors and off-odors.

As used herein, the term, “antioxidant” refers to compounds in food products that scavenge and neutralize free radicals.

As used herein, the term “quality of food” or “food quality” refers to the sum of all properties and attributes, such as appearance (including size, shape, color, gloss and consistency), texture, flavor, nutritional content, etc., of the food product that are acceptable to the consumer.

As used herein, the term “phenolic compound” refers a class of chemical compounds consisting of one or more hydroxyl groups (-OH) bonded directly to an aromatic hydrocarbon group.

In the drawings, like reference numerals designate identical or corresponding parts throughout the several views. Further, as used herein, the words “a,” “an” and the like generally carry a meaning of “one or more,” unless stated otherwise.

Furthermore, the terms “approximately,” “approximate,” “about,” and similar terms generally refer to ranges that include the identified value within a margin of 20%, 10%, or preferably 5%, and any values therebetween.

Aspects of this disclosure are directed towards a method for improving a shelf life, oxidative stability and thermal stability of food products. In an embodiment, the food products can include, but are not limited to, edible oils, meat, egg-based food products, baked products, and any combination thereof. In an example, the baked products include cakes, cookies, breads, etc. In another example, the baked product is a vanilla cake. In another embodiment, the present disclosure is directed to preserving color of fruit and/or vegetable juices using a coconut pairing residue extract (CPRE). The coconut paring residue extract (CPRE) (residue remaining after expulsion of paring oil from coconut parings) is a rich source of phenolic antioxidants. An ethanolic, a methanolic, or an aqueous or other polar solvent extract of a coconut paring residue contains mainly a mixture of phenolic antioxidants. The phenolic antioxidants from the CPRE may be introduced as a low-cost natural source of antioxidants for improving the shelf life of food products.

Referring to FIG. 1, a statistical representation of antioxidant activities of CPRE and synthetic antioxidants, butylated hydroxytoluene (BHT) and butylated hydroxyanisole (BHA), by various antioxidant assays are illustrated. FIGS. 1A-1C represent determination of an antioxidant activity by a 2,2-diphenyl- 1-picrylhydrazyl (DPPH) radical scavenging activity (FIG. 1 A), a ferric reducing antioxidant power (FRAP) assay (FIG. IB) and an inhibition of deoxyribose degradation (FIG. 1C) at 30 microgram per milliliter (pg/mL) concentration of phenolic substances.

FIG. 1 A represents the ability of antioxidants to scavenge DPPH radical determined according to the method of Hatano et al. (1988). From FIG. 1 A it can be observed that BHA had the similar ability to scavenge DPPH free radicals, which was slightly higher than the known antioxidant BHT and ethanolic extracts of the coconut paring residue extract (CPRE). While 52.5% of inhibition was noted for BHA, 30% inhibition was observed by BHT, and 40% inhibition was observed by CPRE. From FIG. IB it can be observed that CPRE showed better ferric reducing ability compared to synthetic antioxidants. 125.2% ferric reducing ability was observed in CPRE compared to 95.9% and 101.2% in BHT and BHA respectively. The results suggest that CPRE has an antioxidant activity either comparable or better than the synthetic antioxidants known in the market.

FIG. 1C represents the inhibition of deoxyribose degradation. From FIG. 1C it can be observed that both BHT and BHA show no significant difference in the inhibition of deoxyribose degradation compared to CPRE. 39.5% of the inhibition of deoxyribose degradation was observed in CPRE, 32.6% was observed in BHT and 36.4% was observed in BHA. The values obtained for the antioxidant activity of CPRE was higher for FRAP compared to other methods studied viz. DPPH and deoxyribose degradation assay.

Most of the natural antioxidants are thermally unstable. The thermal stability of the food preservatives is important for the effectiveness of the food preservatives used in cooked food products. Usually, preservatives are added during cooking prior to the heating steps. Temperatures up to 170 °C are common during cooking such as frying and baking. Therefore, the effect of temperature on thermal stability of the antioxidant (CPRE in comparison to BHT and BHA) is described in FIG. 2A and FIG. 2B. For this purpose, the ability of a heat-treated CPRE at 180 °C to protect sunflower oil was tested using a rancimat test. FIG. 2A represents a rancimat test which is repeated with same quantities of CPRE and BHT in both modes, i.e., pre-heating and post-heating mode. Between the pre heating and post heating test, the sunflower oil with the extract was heated at 180 °C for 2 hours. Both BHT and CPRE retain over 90% of their initial stability after heating for 2 hours at 180 °C, suggesting that the thermal stability of CPRE comparable to the synthetic antioxidants. FIG. 2B and FIG. 2C represent a protection factor at room temperature and 180 °C for 2 hours respectively. CPRE shows more stability than the BHT and BHA under both these conditions. FIG. 2D represents a retained stability graph after the antioxidants undergo both the conditions (exposure to room temperature and at 180 °C for 2 hours). It was observed that 95% of initial stability was retained with CPRE even after heating for 2 hours at 180 °C, while 93% is retained in BHA and 88% is retained in BHT, suggesting the CPRE of the present disclosure is thermally stable at high temperatures.

One of the main pathways of degradation of meat food products is oxidation of fat present in the meat, producing the corresponding degraded oxidation products. As secondary oxidative products are stable and more clearly indicate the expiry of the shelf life by their formation, secondary oxidation products, such as, thiobarbituric acid reactive substances (TBARS) are monitored as a marker indicating a degree of deterioration of meat. FIG. 3 A represents prepared cooked pork samples. FIG. 3B represents both CPRE and BHT inhibiting TBARS formation in pork and inhibition values of CPRE are comparable to those of BHT with no statistically significant difference between the synthetic antioxidant and CPRE.

FIG. 3B further represents formation of TBARS as a malondialdehyde per kg meat with time in cooked pork samples. There is no statistically significant difference between the cooked pork samples with CPRE and the cooked pork samples with BHT based on analysis of variance (ANOVA) followed by post-hoc Tukey’s test. Each data point represents mean ± standard deviation (SD; n =3).

Referring to FIG. 4, the effect of concentration of BHT and CPRE on percentage inhibition of TBARS formation in egg yolk homogenates is described. (P <0.05) is considered a statistically significant difference based on ANOVA followed by post-hoc Tukey’s test. There is no statistically significant difference between the cooked pork samples with CPRE and the cooked pork samples with BHT. Each data point represents mean ± SD (n =3). Egg yolk homogenate is a lipid-rich food model system for the evaluation of a lipid oxidation. Egg yolk contains linoleic acid as the major polyunsaturated fatty acid, which deteriorates by oxidation forming TBARS. The results in the FIG. 4 suggests that CPRE is a successful replacement for BHT for the preservation of egg-based food products. There was no statistically significant difference between the TBARS level in the egg yolk homogenate samples with CPRE or the synthetic antioxidant BHT at the tested concentrations.

Referring to FIG. 5, the effect of the antioxidants (CPRE, BHT, and a control) on percentage inhibition of a b-carotene bleaching, with time, in fruit and vegetable juices is described. The corrected absorbance values at 450 nm are significantly (P <0.05) higher in the fruit and vegetable juice samples with CPRE compared to BHT based on ANOVA followed by post-hoc Tukey’s test suggesting a higher protective effect from addition of CPRE. Each data point represents mean ± SD (n =3). Inhibition of the oxidative deterioration of plant pigments such as an anthocyanin or b-carotene by phenolic antioxidants is important to preserve the nutritional quality and the color of fruit juices or vegetable juices (Roidoung et ah, 2016). The b -carotene linoleic acid emulsion system was used to test the effectiveness CPRE to protect the color of the juices. Linoleic acid forms peroxides and these peroxides bleach the color of plant pigments. The peroxide bleaching is inhibited by antioxidants. The potential of phenolic antioxidants to inhibit a bleaching of pigment color, such as b-carotene, may be used to evaluate the potential of antioxidants to preserve the color of fruit juices or vegetable juices. In the presence of antioxidants, the oxidation of b-carotene by hydroperoxides is minimized. The potential of CPRE to inhibit the bleaching of color in fruit and vegetable juices was evaluated in the present experiment. Both CPRE and BHT inhibit the bleaching of the color of juices in comparison to the control with no added antioxidants. It was observed that the protective effect is significantly (P <0.05) higher in CPRE compared to BHT.

The peroxide value is a useful indicator of determining the early stage of oxidation of fatty acids. The effects of the antioxidants on formation of peroxides in cake samples during storage at room temperature is given in FIG. 6. Detection of peroxide gives the initial evidence of the rancidity in unsaturated fats and oils. The amount of the peroxide value of fats indicates the degree of primary oxidation and therefore its likeliness of becoming rancid. A lower peroxide value indicates a good quality of oil and a good preservation status. From the FIG. 6, it is evident that CPRE shows lower number of the peroxide value than the BHT and control indicating that it is a good qualitative oil and a food preservative.

Referring to FIG. 7, the effect of antioxidants (CPRE, BHT, and the control) using a hexanal as an index of the lipid oxidation, in the baked vanilla cakes is described. For this purpose, headspace solid phase microextraction gas chromatography (SPME-GC) was used to analyze levels of hexanal as an indicator of the formation of secondary oxidation products. When a hexanal concentration in low-fat dehydrated food products increases above 5 ppm, rancid odors were observed. However, hexanal concentrations above 0.3 ppm were found to affect the sensory quality. From the experiment performed, it was observed that the CPRE-added cake samples maintained hexanal levels below 0.3 ppm up to at least 14 days of storage at room temperature, indicating a higher protective effect of CPRE.

Referring to FIG. 8, a statistical representation comparing the effect of the antioxidants (CPRE, BHT, and the control) on physical parameters in cakes is described. Physical parameters (in percentage) considered for evaluation are a moisture content, a porosity, a crumb density, a pore area, and color, that affect consumer preference. Therefore, the moisture content, the porosity (as a measure of volume), the pore area, the crumb density, and the cake color were analyzed for the control, the BHT-added and CPRE-added cakes in order to check if the added antioxidants cause any changes to the structure of cakes, thus, consumer acceptability. Results show that the moisture content and the porosity of the fresh cakes are not significantly different in the cake samples containing different antioxidants on comparison with the control. The crumb density reflects the cell size of cakes. The crumb density of the antioxidant-added cakes is not significantly different than the control cake. Increase of the crumb density improves the brightness, decreases the cell size and cell wall thickness, and increasing the crumb firmness in bread. The fourth graph from left shows that there is no significant difference among the pore areas of the cake samples, indicating that added antioxidants may not affect the pore size of cakes. The color of cakes is an important parameter that affects consumer preference. The color space components represent lightness and darkness (L*) varying from lightness (+L*) to darkness (- L*), there is no significant difference among the color space components in the control and cakes with different antioxidants. In addition to physical parameters, it is important to evaluate the sensory quality of cakes using a trained panel as a more practical indicator of the sensory quality. The sensory quality evaluation was conducted within the period at which the maximum allowable microbial activity is not exceeded. Sensory parameters like taste, aroma, texture, and color are represented on day 1, day 6 and day 10 for control, BHT and CPRE. Referring to FIG. 9, a statistical representation comparing the effect of the antioxidants (CPRE, BHT, and the control) on a sensory quality in cakes, over a period, is described. No significant difference (p < 0.05) in the scores was observed for all the tested sensory qualities in the control and all other cake samples on day 1. On day 6, it is observed that there is significant difference in the taste, aroma, texture, color and overall sensory parameters for control, BHT and CPRE. Cake samples with CPRE showed better taste, aroma, texture and color in comparison to the cake samples having BHT and control. A significant decrease (p < 0.05) in sensory scores was observed in the control samples on day 6, which possibly is due to formation of volatile compounds. On day 10, significant difference is observed in taste and aroma for cake samples with CPRE and BHT. Cake samples with CPRE showed better taste and aroma than cake samples with BHT. Texture, color and overall sensory parameters show no significant difference. However, cake samples with CPRE showed slightly better texture and overall parameters; color was found to be slightly better in cake samples with BHT than the cake samples with CPRE. Most sensory scores for all the cake samples are significantly high (p < 0.05) on day 1 compared with later dates. However, CPRE added cakes retained sensory quality from day 6 to day 10.

Referring to FIG. 10, a statistical representation of microbial shelf life of the antioxidant added cakes is described. The microbial shelf is life based on the time taken to exceed an aerobic plate count (APC), and yeast and mold count (YMC). For control (cake with no added antioxidants) the microbial shelf life was found to be 7 days, while BHT- added cake samples exceeded the APC and YMC levels on day 11. CPRE added cake samples took 13 days to exceed the APC and YMC levels. Therefore, BHT and CPRE appear to have an antimicrobial activity in comparison to the control, even after exposure to high temperature during the baking process. CPRE showed higher antimicrobial activity compared with BHT. The antimicrobial activity of the phenolic compounds present in CPRE may contribute to the extended microbial shelf life of the antioxidant-added samples. Assuming that the chemical rancidity may be tolerated, the quality of cake is still not acceptable by day 7 due to high microbial levels. In agreement with the reported observations, it was observed that the microbial shelf life is of higher concern than the chemical rancidity for high-moisture bakery products such as cake. Therefore, the extension of both the microbial shelf life and the chemical shelf life by CPRE are important for the extension of the overall shelf life of cakes. As such, CPRE may serve as the thermally stable natural alternatives to synthetic antioxidants for preservation of cakes by extending both chemical and microbial shelf life.

The CPRE is a cost-effective by-product generated in the desiccated coconut industry. These extracts may be introduced as a low-cost natural source of antioxidants for improving the shelf life of food products. The present disclosure describes the effect of CPRE in extending the oxidative stability of edible oils, meat, egg-based food products, baked products, and colour stability of fruit and vegetable juices. As a result, it was found that CPRE significantly (P<0.05) increases the shelf life of edible oils, meat, egg-based food products, baked products; and was also found to be effective in preserving the colour stability of fruit and vegetable juices. Therefore, antioxidant mixtures from CPRE are thought to be an effective food preservative.

Extracts of coconut paring residue can improve the shelf life of food emulsions, meat and polyunsaturated oils. Phenolic antioxidants responsible for these food stabilizing effects have high thermal stability. Thermal stability is an important parameter to be considered in evaluating the effectiveness of antioxidants in food systems. Most of the bakery and processed-food industries require the addition of antioxidants to food in order to protect food from deterioration during processing and storage. Loss of antioxidants at high temperatures is due to both evaporation and decomposition of antioxidants. The proposed CPRE show higher thermal stabilities compared to synthetic antioxidants BHT, and BHA. Use of CPRE as a food preservative is a low-cost method. Therefore, the extracts of coconut paring residue can be developed as commercial natural antioxidant preparations with potential applications in food industry.

EXAMPLES

The disclosure will now be illustrated with working examples, which is intended to illustrate the working of disclosure and not intended to take restrictively to imply any limitations on the scope of the present disclosure. The working examples depict the effect of CPRE on shelf life, thermal stability, and oxidative stability of food products.

EXAMPLE 1

Extraction of phenolic antioxidants from a coconut paring residue

Ethanol/water (70:30 v/v, 10 milliliter (mL)) was mixed with a powdered coconut paring residue (10.0 grams or g) and the mixture was agitated using a vortex at 40 Hertz (Hz) for 2 minutes (min) (twice). The mixture was centrifuged (1080 g, 10 min) and the resultant clear solution was separated. This procedure was repeated 4 times for the same coconut paring residue sample with fresh 10 mL portions of the solvent system (ethanol/water (70:30 v/v). The resultant coconut paring residue extract (CPRE) was collected, diluted to 50.0 mL and stored in a dark brown vial under nitrogen. The CPRE was further concentrated to ~ 35 % (w/v) concentration by evaporating the water (solvent) after extracting at 3-5 % (w/v) (CPRE concentrate) until further experiments were carried out

EXAMPLE 2

Determination of a total phenol content

The total phenolic content in CPRE was determined according to the method of Singleton & Rossi (1965). CPRE (100 microliters (pL) was mixed with diluted Folin Ciocalteu reagent (2.5 mL). After 5 min, 7.5 % Na2CCh solution (2.0 mL) was added, and the mixture was diluted to 5 mL by adding distilled water. After 1 hour, the absorbance of the reaction mixture was measured at 765 nm using Multiscan Go Spectrophotometer (Thermo Scientific) with respect to a blank with no added phenolic extract. The total phenolic content was expressed as gallic acid equivalents (GAE). Calorimetrically determined phenolic concentration of the CPRE was adjusted to a concentration series (20, 40, 60, 80 pg/ mL) with the solvent system (ethanol: water 70:30 volume/volume (v/v)) and the reducing power was determined according to the procedure explained by Oyaizu (1986). Phenolic extracts (50 pL) at various concentrations, and phosphate buffer (pH 6.6, 0.2 M, 2.5 mL), were added to potassium ferricyanide (10.0 mg/mL, 2.5 mL) and the reaction mixture was incubated at 50 °C for 20 min. Then, trichloroacetic acid (TCA) (10%, 2.5 mL) was added, and the mixture was centrifuged (1080 g for 10 min). The supernatant (2.5 mL) was mixed with distilled water (2.5 mL) and FeCb (1.0 mg/ mL, 0.5 mL). Then the absorbance was measured at 700 nm using a UV-visible spectrophotometer. The assay was performed similarly for a concentration series of 20 pg/mL to 80 pg/mL solutions of butylated hydroxytoluene (BHT). The reducing power was calculated according to the following formula:

Reducing power % = [(Ai/ Ao) ¹ ] x 100

(Ai = Absorbance of the reaction mixture with phenolic extract or BHT, Ao = Absorbance of the reaction mixture with the solvent system without phenolic extract or BHT).

EXAMPLE 3 Antioxidant activity

2,2-diphenyl- 1-picrylhydrazyl (DPPH) radical scavenging activity of CPRE was measured according to the method of Hatano et al. (1988). The total phenolic content of CPRE was adjusted to the required concentrations by diluting with the same solvent system used for the extraction. Each phenolic extract (50 pL) of various concentrations (20, 40, 60 and 80 pg/mL) was added to a methanolic solution of a DPPH (0.3 mL, 0.8 mM) and the total volume was adjusted to 3 mL. The resultant mixture was further vortexed at 40 Hz for 5 min. After 30 min of incubation at room temperature in the dark, the absorbance of each reaction mixture was measured at 517 nm. The DPPH radical scavenging activity was measured similarly for a series of 20 to 80 pg/mL solutions of BHT. The inhibitory effect of the DPPH radical was calculated according to the following formula:

Inhibition % = [(Ao - Ai)/Ao] x 100 where Ao = absorbance of the reaction mixture with solvent system instead of phenolic extract or BHT, Ai= absorbance of the reaction mixture with phenolic extract or BHT.

EXAMPLE 4

Protection of edible oils against oxidation by CPRE

Naturally present antioxidant compounds of sunflower oil were removed (antioxidant stripped) according to the method reported by Fuster et al. (1998). A glass column (40 ^c 2.5 cm) was packed with 70 g of alumina (activated at 100 °C for 8 h and then 200 °C for 12 h) suspended in hexane and capped with sea sand (2.0 g). The column was conditioned by pre-washing with hexane (200 mL). Sunflower oil (100 mL) was dissolved in hexane (100 mL) and passed through the column. The column was further washed with hexane (200 mL), and the eluent was collected and evaporated using a rotary evaporator to remove the solvent. The antioxidant-stripped oil was stored at -20 °C for further analysis.

The required volume of CPRE in aqueous ethanol to reach 200 pg/g in sunflower oil was transferred to a reaction tube of the Rancimat apparatus. Commercial antioxidants (BHT, butylated hydroxyanisole (BHA) and tocopherol) required to obtain 200 pg/g in sunflower oil was dissolved in aqueous ethanol and transferred into reaction tubes. The solvent in each tube was evaporated under a stream of nitrogen. Then an antioxidant- stripped sunflower oil (3.2 g) was added to each tube and vortexed at 40 Hz for 2 min. The induction time (IT) was further evaluated in each tube at air flow rate of 20 L/h at 100 °C in a Rancimat apparatus (Metrohm 892 Professional Rancimat, Herisau, Switzerland). The time taken to achieve the conductivity of 30 pS/cm was taken as stability time. Time taken for oxidation products to first appear was taken as the induction time. Stripped sunflower oil (3.2 g) without added antioxidants was used as the control. Results of the antioxidant added oils were also reported as protection factor (PF):

PF = (IT antioxidant added oil / IT control).

EXAMPLE 5

Thermal stability of CPRE

A Rancimat test was repeated with same quantities of CPRE and BHT after heating the two at 180°C for 2 hours.

EXAMPLE 6

Preservation of cooked meat by CPRE

The effectiveness of CPRE on delaying oxidation of pork as a muscle food was determined by measuring the thiobarbituric acid reactive substances (TBARS) as secondary oxidation product using a modified version of the method described by Wettasinghe and Shahiidi (1999). For this purpose, ground pork was mixed with deionized water (20% w/w). CPRE or BHT (200 pg/g of meat) were added separately to pork samples and thoroughly homogenized. A control sample without added any antioxidant was also prepared. Samples were cooked in a water bath at 80 ± 2 °C for 40 min while stirring every 5 min with a glass rod. After cooling to room temperature, the meat was homogenized, weighed in 2.00 g portions, and transferred into polythene bags. The meat samples were then stored in a refrigerator at 4 °C for 14 days. Samples of 2.00 g portions were taken on days 0, 5, 7 and 14 and were analyzed for TBARS.

EXAMPLE 7

Preservation of egg-based food products by CPRE

A modified method by Kuppusamy et al. (2002) was used to determine TBARS formation during the lipid peroxidation of egg yolk. For this purpose, an egg yolk emulsion (25g/L) was prepared in phosphate buffer (pH 7.4, 0.1 M). To this emulsion (1.0 mL) and Fe ²⁺ (1000 mM, 100 pL) were added. CPRE to obtain final phenolic concentrations of 0.125 pg/ mL, to 16 pg/ mL was added from a stock solution and the total volume was adjusted to 1.5 mL with ethanol: water 70: 30 (v/v). Then, the reaction mixture was incubated at 37 °C for 1 hour. The incubated mixture was treated with freshly prepared TCA (15%, 0.5 mL) and thiobarbituric acid (1%, 1.0 mL). The reaction tubes were kept in a boiling water bath for 10 min. The contents of the tubes were cooled to room temperature and centrifuged (3500 g x 10 min). The formation of TBARS was measured by removing supernatant (100 pL) and measuring the absorbance at 532 nm.

The buffered egg yolk emulsion without added phenolic extract was used as a control. The percentage inhibition was calculated from the following equation:

Percentage inhibition = [1- (Asampie/ Ao)] x 100

(Asampie = Absorbance of the sample, Ao = Absorbance of the control).

EXAMPLE 8

Preservation of the color of fruit juices and vegetable juices by CPRE

Protection of the color of b-carotene was evaluated in a b-carotene linoleate model system as explained by Wettasinghe & Shahidi (1999) with some modifications. A mixed fruit juice was prepared by mixing mango and papaya. The mixture was centrifuged and the absorbance of the juice at 450 nm was adjusted to around 0.3-0.4 absorption units. The colored clear liquid (50 mL) was evaporated under vacuum. To the residue, linoleic acid (20 mg), Tween 20 emulsifier (400 mg) and aerated distilled water (50 mL) were added to the flask with vigorous shaking. CPRE, to a final concentration of 60 pg/mL (20 pL) was manually pipetted into sample wells of a 96 well assay plate, and b -carotene-linoleic acid emulsion (200 pL) was added to each well. The same procedure was repeated for carrot juice. The microplate was incubated at 45 °C and absorbance was read at 450 nm using a microplate reader (MultiSkan GO, Microplate spectrophotometer, Vantaa, Finland).

Before taking each reading the microplate reader was programmed to have 10 seconds (s) shaking. Readings of the samples were recorded immediately at zero time and at every 30 min thereon to up to 120 min. BHT at 15, 30, 60 pg/mL were used for comparison. An equal amount of ethanol: water (70:30 v/v) solvent system was used for the control. Blank samples without juice samples were prepared for background subtraction.

Statistical analysis

All analyses were run in triplicate unless otherwise indicated. An analysis of variance (ANOVA) followed by two sample t-test for pairwise comparisons was carried out for the determination of significant differences (p<0.05) between the means. Data were analyzed using Mini tab (Version 17 for Windows).

RESULTS AND DISCUSSION

Extraction of phenolic antioxidants from a coconut paring residue and determination of a total phenol content and an antioxidant activity

The total phenolic content of a coconut paring residue extract (CPRE) is 2527 ± 51 GAE mg/ kg coconut paring residue. The results indicate that coconut paring residue extract is a rich source of natural antioxidants. An antioxidant activity was determined by FRAP and DPPH for a BHT and CPRE as a preliminary step to evaluate the antioxidant potential of CPRE compared to the synthetic antioxidants. The results are given in the Table 1.

Table 1 : Antioxidant activity of CPRE and BHT

Data presented as mean + SD (n = 3). Different letters a, and b in each category indicate significant difference (P < 0.05) in columns based on students t-test. From Table 1, it can be observed that FRAP of CPRE is higher than that of BHT at 20-80 pg mL ^_1 concentration range. There was no significant difference in the DPPH radical scavenging activities of BHT and CPRE at 20-60 pg mL ^_1 range, as reflected by percentage inhibition. DPPH radical scavenging activity is significantly higher at 80 pg mL-1 for CPRE.

Protection of edible oils against an oxidation by CPRE

Polyunsaturated oils easily form peroxides and volatile oxidation products: The resultant rancid oils are not suitable for human consumption. Peroxide formation may be retarded by natural antioxidants. In the present experiment, highly polyunsaturated sunflower oil was selected. The protective effect of CPRE against the oxidation of sunflower oil was tested under accelerated oxidation conditions using Rancimat apparatus. An Induction time and a protection factor (Induction time with respect to control) are given in Table 2. The results indicate that CPRE provides more protection to sunflower oil against oxidation compared to common synthetic antioxidants such BHT and BHA.

Table 2. Protection of sunflower oil by antioxidants

Data presented as mean ± SD (n =3). Different letters a, b and c indicate significant difference (p<0.05) in a column based on ANOVA followed by Tukey’s post-hoc test for pairwise comparisons.

Thermal stability of CPRE

Most of the natural antioxidants are thermally unstable. A thermal stability of the food preservatives is important for the effectiveness of the food preservatives used in cooked food products. Usually, preservatives are added in a baking and a cooking prior to the heating. Temperatures up to 170 °C is common in the frying, cooking and baking. Therefore, the ability of heat-treated CPRE at 180 °C to protect sunflower oil was tested using a Rancimat test. Both BHT and CPRE retain over 90% of their initial stability after heating for 2 hours at 180 °C (Table 3).

Table 3. Protection of sunflower oil by heated antioxidants

Data presented as mean ± SD (n =3). Different letters a, b and c indicate significant difference (p<0.05) in a column based on ANOVA followed by Tukey’s post-hoc test for pairwise comparisons.

Effect of CPRE on the oxidative stability of meat

Meat products are easily deteriorated upon storage. One of the main pathways of degradation of meat food products is the oxidation of fat present in the meat, producing oxidation products. As secondary oxidative products are stable and more clearly indicate the expiry of the shelf life by their formation, secondary oxidation products, thiobarbituric acid reactive substances (TBARS) were monitored as a marker for degree of deterioration of meat. Prepared cooked pork samples are indicated in FIG. 3 A. As shown in FIG. 3B, both CPRE and BHT inhibit the formation of TBARS in pork and inhibition values of CPRE are comparable to those of BHT with no statistically significant difference between the synthetic antioxidant and CPRE.

Preservation of egg-based food products by CPRE

Egg yolk homogenate is a lipid-rich food model system for the evaluation of lipid oxidation. Egg yolk contains linoleic acid as the major polyunsaturated fatty acid, which deteriorates by oxidation forming TBARS. The results in the FIG. 4 suggests that CPRE is a successful replacement for BHT for the preservation of egg-based food products. There was no statistically significant difference between the TBARS level in the egg yolk homogenate samples with CPRE or the synthetic antioxidant BHT at the tested concentrations. Preservation of the color of fruit juices and vegetable juices by CPRE

Inhibition of the oxidative deterioration of plant pigments such as anthocyanin or b- carotene by phenolic antioxidants is important to preserve the nutritional quality and the color of fruit juices or vegetable juices (Roidoung et al., 2016). The b -carotene linoleic acid emulsion system was used to test the effectiveness CPRE to protect the color of the juices. Linoleic acid forms peroxides and these peroxides bleach the color of plant pigments. This bleaching is inhibited by antioxidants. The potential of phenolic antioxidants to inhibit bleaching of the color of pigments such as b-carotene can also be used to evaluate the potential of antioxidants to preserve the color of fruit juices or vegetable juices. In the presence of antioxidants, the oxidation of b-carotene by hydroperoxides is minimized. The potential of CPRE to inhibit the bleaching of color of fruit and vegetable juices was evaluated in the present experiment. Both CPRE and BHT inhibit the bleaching of the color of juices compared to a control with no added antioxidants (CPRE or BHT) and the protective effect is significantly (P <0.05) higher in CPRE compared to BHT (FIG. 5).

INDUSTRIAL APPLICABILITY

The present disclosure provides methods to overcome the limitations in the above- mentioned prior art. In an exemplary embodiment, the present disclosure provides a method for improving a shelf life, oxidative stability and thermal stability of food products. The present disclosure also discloses a method to preserve color of fruit and/or vegetable juices using a coconut pairing residue extract (CPRE). The CPRE is a cost-effective by-product generated in the desiccated coconut industry and can be therefore used as a low-cost natural source of antioxidants for improving the shelf life of food products. Also, since CPRE antioxidant is obtained from natural sources, it is substantially safer for human consumption than synthetic alternatives. Also, CPRE has substantially higher thermal stability, than other conventionally used antioxidants obtained synthetically or from natural sources. Therefore, CPRE extracts are superior food preservatives in food products that require exposure to high temperatures. Also, the extracts of coconut paring residue can be prepared and utilized on an industrial scale as commercial natural antioxidant preparations with potential applications in food industry.

While aspects of the present disclosure have been particularly shown and described with reference to the embodiments above, it will be understood by those skilled in the art that various additional embodiments may be contemplated by the modification of the disclosed methods without departing from the spirit and scope of what is disclosed. Such embodiments should be understood to fall within the scope of the present disclosure as determined based upon the claims and any equivalents thereof.