Field of the invention

The invention relates to a process to prepare a heat-treated intermediate onion preparation for use in industrial food production.

Background of the invention

Ready-to-eat products like meals, soups and sauces are products that only require heating before consumption. These products include stew, fried rice, curries, soups, (pasta) sauce like sauce bolognaise etc. They may be packaged in cans, jars or other packaging.

Many of these products like soups and sauces contain onion. The industrial practice of preparing soups and sauces is relatively straight forward. It generally includes simply mixing onion with the remaining food ingredients like spices, salt, flavour, thickeners, water to form the end-product like a sauce or soup and heating the mixture at about 70°C followed by preservation and filling in suitable containers.

In a domestic kitchen, normally raw onions are used in the preparation of a soup or sauce. In contrast, to produce such ready-to-eat products in an industrial setting, usually onions are pre-processed into what may be called an intermediate onion preparation before it is mixed with the remaining ingredients of the final food product e.g. a soup.

Intermediate ingredients in a food industrial setting refer to ingredients which have been processed but in general are not intended to be sold and consumed as such. In contrast, intermediate ingredients are designed to be used to formulate a so- called end-application, a soup, a sauce or a dish like a stew that will be consumed as such.

However, the flavour is far from what we would expect from a home-cooked version. To improve the flavour of industrially prepared soups, a heat-treated intermediate onion preparation can be made in a separate pre-process by heating onions separately in a so called soffritto tank with a volume of typically 2500-3000 litre wherein 200kg onion is heated at 95°C for 15-30 min. The result is slightly better than the onion prepared at 70°C but often there is so little onion flavour that often onion aroma is added separately to such industrially prepared soup.

JP63-16775 discloses a process to prepare a roasted onion by first drying fresh onion with generally has more than 90wt% moisture down to 30-80wt% moisture. This is followed by sealing the onion in a can and heating the can in a retort. In the food industry retorts refer to large pressure cookers used for the sterilisation step in a canning process. Retorts can be several meters long tunnels with a diameter of about 1.5 meters into which racks with cans can be wheeled in. JP63-16775 discloses to heat the onions for 35 min at 116 °C in a retort and teaches to stay below 130°C to avoid a burnt taste.

JP 2001/190 240 discloses that this process of JP63-16775 results an off- flavour: unpleasant smell typical to high temperature cooking like retort. JP 2001/190 240 aims to overcome such high temperature induced off-flavour. It discloses a process with two separate heating steps. In the first heating step the temperature is lowered compared to JP63-16775: 900 parts of onion and 100 parts of water are heated for 15 min at 109°C and 0.04 MPa (gauge pressure) in a pressure cooker or retort. This is followed by a second heating step in an open frying pan over moderate heat to reduce the onion preparation to about 60% of its weight (600 parts) of thermally treated onion preparation. JP 2001/190 240 teaches to apply the second heating step in the“open system” for the time needed to evaporate the unpleasant smell developed during the high-temperature cooking. The resultant onion product is said to be sweet and free from such unpleasant smell.

Looking for a good tasting intermediate onion preparation, the present applicants have reproduced the process of JP 2001/190 240 and indeed the onion preparation thus prepared was sweet without much off-flavour. However, surprisingly there was also very little onion flavour if any.

Therefore, there remains a need in the food industry for an improved process to pre-process onion into a heat-treated intermediate onion preparation that has a delicious (soffritto / sauteed) onion flavour without the unpleasant off-flavour of e.g. when onion is heated at high temperature in a retort. In addition, it would be desirable to provide a heat-treated intermediate onion preparation which has such an intense onion flavour profile it allows to decrease the amount of onion to be used and even the need to add onion aroma.

Summary of the invention

According to the invention a process is provided for preparing a heat-treated intermediate onion preparation comprising the steps of: a) Providing comminuted onion,

b) Optionally, admixing 0 to 100 parts by weight of a liquid phase to 100 parts of weight of comminuted onion,

c) Heating the comminuted onion in a Heat Up Phase from 25°C to 95% of the Holding Temperature in a Heat Up Time of less than 20 min, preferably less than 5 min; whereby the Holding Temperature is preferably of from 135°C to 180°C, more preferably from more than 140 °C to 170° C, even more preferably from 145°C to 160°C, d) Holding the comminuted onion during the Holding Phase for a Holding Time at the Holding Temperature whereby the Holding phase corresponds to the Holding time and starts at 95% of the Holding Temperature and continues when the temperature increases up to the Holding Temperature and decreases thereafter to 95% of the Holding Temperature, and the Holding Time is from 10 sec to 7 min, preferably 30 sec to 6 min, more preferably 1 to 5 min hereby the pressure during the Holding phase is at least the saturated vapor pressure of water and preferably the level of oxygen is at atmospheric oxygen levels, preferably the heating treatment is such that the comminuted onion is completely sterilised ,

e) Cooling the comminuted onion after the Holding phase to a Filling

Temperature, preferably less than 90°C, preferably less than 80°C, preferably less than 30°C, preferably in a Cooling Time of less than 20 min, preferably less than 15 min, more preferably less than 10 min, preferably between 5 sec and 15 min, more preferably between 30 sec and 10 min.to form the heat-treated intermediate onion preparation, f) Optionally, adding the heat-treated intermediate onion preparation at Filling Temperature, preferably at atmospheric pressure, to process to prepare a food product;

g) Optionally, filling the heat-treated intermediate onion preparation into a container at the Filling Temperature, preferably at atmospheric pressure.

The invention also provides a heat-treated intermediate onion preparation as described below, a process to prepare a food composition comprising the step of adding a heat-treated intermediate onion preparation prepared according to the invention in a process to prepare a food composition and a food composition comprising said heat-treated intermediate onion preparation.

Surprisingly, the present invention provides a process suitable for industrial scale using very high temperatures whereby the heat-treated intermediate onion preparation has a more intense flavour profile without undesirable off-flavour of onion heated at high temperature. The flavour of the inventive heat-treated intermediate onion preparation is so intense that it allows to decrease the amount of comminuted onion, additional onion aroma, salt and consequently the environmental resources.

Whilst JP63-16775 also discloses a single heating step to produce an heat- treated onion preparation, it differs from the present invention because JP63-16775 does not directly and unambiguously discloses a specific heat up time of the retort process. Using an industrial retort the heat up time starting from room temperature to reach a holding temperature of 120°C will generally be at least 35 min. JP63-16775 also teaches away from using temperatures over 130°C.

JP 2001/190 240 teaches away from using a single heating step as in the present invention as JP 2001/190 240 discloses the need for a second heating step in an open frying pan to evaporate the off-flavour developed in the first heating step. Surprisingly, even though the present invention applies a higher Holding Temperature than JP63-16775 i.e. higher than 130°C the intermediate onion preparation according the present invention shows no undesirable off-flavour that needs to be removed by a second heating step. Although JP 2001/190 240 discloses a maximum Holding Temperature of 140°C, we note that the corresponding Heat Up time is not disclosed directly and unambiguously.

Detailed description of the invention

The process according to the invention comprises a single heating step carried out under the conditions described herein. The single heating step has three consecutive phases: a Heat Up Phase, a Holding Phase at a Holding Temperature and a Cooling phase. As known in the art of food processing, heating a product is a dynamic process and the temperature of the heating means may not correspond to the temperature of the food to be heated. For example, milk can be sterilised with steam injection. The temperature of the steam can be up to 160°C. However, to sterilise milk the steam injection only needs to heat the milk to 135°C for 1 -2 seconds. Thus, the food product is only heated to 135°C while the steam is much hotter. In the present invention the temperature such as the Holding Temperature relates to the temperature of the onion as measured with temperature probes inside the heating device.

In a first step of the invention, comminuted onion is provided. This can be fresh or frozen onion. The onion may be used as such or optionally admixed with a liquid phase in a w/w ratio of 0 to 100 parts by weight of a liquid phase to 100 parts of weight of comminuted onions. The liquid phase may be water, oil and a mixture thereof. Any food grade oil may be used such as sunflower oil, olive oil, canola oil etc. Preferably the ratio is 0 to 100 parts of liquid phase to 100 parts of comminuted onion is from 5 to 100 parts, more preferably from 10 to 100 parts of liquid phase to 100 parts of comminuted onion. Whether the comminuted onion is mixed with liquid phase or not it may also be referred to as“onion preparation” for the present purpose. Depending on the desired flavour in the soup, sauce or dish wherein the intermediate onion preparation will be used, a skilled person may find it useful to add e.g. some ginger or spices like curry.

The comminuted onion is then heated in the Heat Up Phase from ambient temperature (25°C) to 95°C The corresponding Heat Up Time is the time needed to heat the comminuted onion from 25°C to 95% of the Holding temperature. The Heat Up Time is preferably less than 20 minutes, more preferably less than 8 minutes, even more preferably less than 5 minutes. The Holding Temperature is preferably more than 135°C to 180°C, more preferably from more than 140 °C to 170 °C, even more preferably from 145°C to 160 °C.

After the Heat Up Phase, the comminuted onion is held during the Holding Phase for a Holding Time at the Holding Temperature. The Holding phase

corresponds to the Holding time and starts at 95% of the Holding Temperature and continues when the temperature increases up to the Holding Temperature and decreases thereafter to 95% of the Holding Temperature. The Holding Time is preferably 10 sec to 7 min, preferably 30 sec to 6 min, more preferably 1 to 5 min such that the comminuted onion is sterilised whereby the pressure during the Holding phase is at least the saturated vapor pressure of water (corresponding to 0.36 to 1.0 MPa gauge) and the level of oxygen is at atmospheric oxygen levels. The Holding phase ends when the subsequent Cooling phase starts. Preferably, the heating treatment is such that the comminuted onion is completely sterilised.

The Cooling Phase corresponds to the Cooling Time which starts when the temperature has returned to 95% of the Holding Temperature and stops at the Filling Temperature. The Filling Temperature is preferably below the atmospheric boiling point of the onion, preferably less than 90°C, preferably less than 80°C, preferably less than 30°C, preferably between 10°C and 90°C, more preferably between 10°C and 80°C preferably between 10°C and 30°C. The Cooling Time is preferably less than 20 min, preferably less than 15 min, more preferably less than 10 min, preferably between 5 sec and 15 min, more preferably between 30 sec and 10 min. The Filling Temperature depends on how the heat-treated intermediate onion preparation is used. Advantageously, the heat-treated intermediate onion preparation can be added at Filling Temperature to a process to prepare a food product like a soup or sauce. For example, the cooled heat-treated intermediate onion preparation may be transported through a pipe and added directly in a vessel with the remaining ingredients of a soup or sauce wherein the soup or sauce is normally prepared. In that case the Filling Temperature may be about 72°C or higher if it is desired that the heat-treated intermediate onion preparation is remains aseptic. Preferably, the addition of the heat-treated intermediate onion preparation is carried out atmospheric pressure.

It may also be desirable to prepare the heat-treated intermediate onion preparation at a different time or location than the production of the food product like a soup or sauce. Then the heat-treated intermediate onion preparation may also be filled into a container at the Filling Temperature and stored before being used, e.g. in an aseptic bag in box to store it at ambient temperatures. Filing is preferably at atmospheric pressure.

Thus, after the Holding Phase, the comminuted onion is cooled to the Filling Temperature for a Cooling Time as described above to form the heat-treated intermediate onion preparation.

Preferably the onion is heated using ohmic heating, steam injection heating or thermal conductive heating.

Preferably, the inventive process does not comprise a step whereby the onion is heated in an open system to reduce the amount of intermediate onion preparation to less than 65% of its weight when compared to the weight of the intermediate onion preparation before the heating in the open system bleating in an open system is a heating step in an open container which allows water to be evaporated thereby reducing the weight of the intermediate onion preparation like heating in open frying pan over moderate heat. Preferably, the inventive process does not comprise a step whereby the onion is heated in an open system at a temperature of from 80°C to 100°C for 3-30 minutes. Preferably, the inventive process does not comprise a step whereby the onion is heated in open system at a temperature of from 80°C to 100°C for 3-30 minutes, thereby reducing the amount of intermediate onion preparation to less than 65% of its weight when compared to the weight of the intermediate onion preparation before the heating in the open system. In contrast, the process according to the invention is normally carried out whereby no substantial amounts of water are evaporated.

Heat-treated intermediate onion preparation

The inventive heat-treated intermediate onion preparation as prepared in the examples had a soft appearance, almost pasty, although distinct onion pieces were still visible. The heat-treated intermediate onion preparation according to the invention preferably comprises at least 0.01 microg/g of disulphide methyl propyl per dry weight of heat-treated intermediate onion preparation, preferably from 0.01 to 6 microg/g of disulphide methyl propyl per dry weight of heat-treated intermediate onion preparation. Preferably, the heat-treated intermediate onion preparation is prepared according to the process described herein.

Measurement of disulphide methyl propyl (DSMP)

DSMP was measured using static Head-Space Gas Chromatography - Mass Spectrometry (sHS-GC-MS). Approximately 10 gram of (frozen) sample was placed in a 20 ml_ head-space vial and homogenized using an ultra-turrax. Head-space equilibration was performed at 60 ^° C for 30 minutes under mild shaking. 500 pl_ of the head-space were injected in the split mode (split ratio 25:1 ) at 250 pl_/s and an injector temperature of 200 ^° C. Syringe temperature was 80 ^° C. The GC column was a 30 m x 250 pm x 1.4 pm Restek Rtx-624 column programmed from 35 ^° C (1 min) to 205 ^° C (2 min) at 10 ^° C/min. Carrier gas was helium at 1 mL/min. The mass spectrometer was operated in the full scan mode at 70 eV ionization energy scanning the mass range from m/z 29 to 300. Temperatures of the transfer line, ionization source and quadrupole were 240 ^° C, 230 ^° C and 150 ^° C, respectively. Quantification was performed using the internal standard method (internal standard

dibutoxymethane). Calibration lines were prepared in water/sunflower oil 1 :1 (v/v) or in water/sunflower oil 19:1 (v/v), depending on the matrix of the sample to be analysed.

Process Equipment

While the applicants did not use a standard retort to carry out the invention using the combination of specific parameters, other standard equipment can be used. The present invention has the advantage that a skilled person - with the knowledge of the required process parameters of the invention - can select appropriate equipment from standard food industry appliances to carry out the invention. The invention can be used in conjunction with standard processing lines without the need for personnel to work at supra-atmospheric pressures.

The process according to the invention can be applied in batch or continuous mode. One example of a batch mode was used for Examples 3 and 4 below when applicants used a steel tube of 10 mm inner diameter and 12 mm outer diameter and about 15-20 cm long which was immersed in oil at the Holding Temperature. The cooling was carried out by taking the tube out the hot oil and cooling it in water to the Filling Temperature. Such a relatively small set up can be used when only small volumes are needed. In continuous mode, the process according to invention may be carried out in suitable heat exchangers capable of reaching the combination of the short Heat-Up Time and the high Holding Temperature. These include scraped surface heat exchangers, Tube in Tube Tube, Annular Tube Tube, Shell and tube exchanger, spiral heat exchanger. Preferably, the onion is heated in a tube in tube in tube heat exchanger, a tubular heat exchanger, helical coil heat exchanger or in a scraped surface heat-exchanger. Such heat exchangers are for example available from Alva Laval. Preferably, in the process according to the invention the onion is heated in a tube having a hydraulic diameter of from 0.1 to 10 cm, preferably less than 0.4 to 5 cm, more preferably of from 0.6 to 3 cm.

The hydraulic diameter, DH, is a commonly used term when handling flow in non- circular tubes and channels. It is defined as: 4

P

Where

• A is the cross-sectional area,

• P is the wetted perimeter of the cross-section

For example for a circular tube: DH=D (wherein D is the tube diameter).

For an annulus: D _H =D _0Ut -Di _n (whereby D _m represents the diameter of the inner tube; D _out represents the diameter of the outer tube)

Without wishing to be bound by theory it is thought that the combination of the short Heat Up Time and the short Holding Time at the relatively high Holding temperature results in the unexpected advantages. Using standard industrial retorts this combination is not known. While heating at temperatures of 140-180°C can be achieved in e.g. a retort under pressure, the heat-up time of a retort to reach 120 °C is at least 50 min. A domestic pressure cooker is not designed to reach temperatures higher than 115 or 117°C.

The invention also provides a food composition comprising a heat-treated intermediate onion preparation prepared according to the invention preferably in an amount of 0.1 to 50 wt% by weight of the total food composition, preferably the food composition is a soup, a sauce or a dish.

The invention also provides a process for preparing a food composition comprising the step of adding a heat-treated intermediate onion preparation prepared according to the invention in a process to prepare a food composition, preferably in an amount of 0.1 to 50 wt% by weight of the total food composition, preferably the food composition is a soup, a sauce or a dish. The invention is further illustrated by the following non-limiting examples. It will be clear to the skilled person how to carry out the invention by using equivalent means without departing from the invention.

Examples

Example 1 JP 2001 190240 (comparative)

An intermediate onion preparation was prepared according the two step heating process of JP 2001 190240. In the first step 900 parts of diced fresh onion and 100 parts water the onion was heated in a standard kitchen 6 L pressure cooker at 109°C for 15 min at 0.14 MPa. (Domestic kitchen pressure cookers are generally designed to reach a maximum temperature of just below 120°C) The Heat Up Time was 16.6 min from 25°C to 109°C. Thereafter, the onion was heated in an open frying pan over moderate heat until the onion was reduced to 60 wt%. The resulting intermediate onion preparation tasted sweet but hardly showed any onion taste.

Example 2 Pan Fried reference (comparative)

An intermediate onion preparation was prepared in a frying pan (e.g. sauteed) by a chef using 50 parts of diced fresh onion and 50 parts of oil. Such a home-cooked version is often considered as the reference for industrially prepared food products. The result was described as having a multi dimension flavour: caramel, sweet, cooked onion and roasty flavour.

Examples 3, 4 and 5 (according to the invention)

Diced fresh onion and oil respectively water was processed as shown in the table below. Examples 3 and 4 were produced in a batch process as described above. Example 5 was produced in a continuous process helical coil heat exchanger and filled in a bag and sealed.

Measurement of disulphide methyl propyl (DSMP)

DSMP was measured as described above.

Example 6 (comparative)

An onion preparation was prepared according the process of JP 2005 061425. 2 kg onions were peeled, cut in pieces, the cut onions put in a pan and heated at 95 °C for 180 minutes, either without a lid (6-A) or with a lid (6-B). The taste of the resulting onion preparations is summarized below: