Fruit Preparations - Development of a New Pressurizing Process

G. Charalambous (Ed.), Off-Flavors in Foods and Beverages © 1992 Elsevier Science Publishers B.V. All rights reserved.

FRUIT PREPARATIONS PROCESS

-

DEVELOPMENT

OF

313

A

NEW

PRESSURIZING

Y. HORIE Meidi-ya Food Factory Co., Ltd., 1-13, Nishigawara 3-Chome, Ibaraki-shi, Osaka, 567 (JAPAN) SUMMARY A new method of processing fruit preparations was developed by high pressurization at 400-600 MPa. Jam and other preparations processed by this method maintain their original fresh fruit color and flavor. 957G of the vitamin C in fresh strawberries was preserved in the pressure-processed jam. Sterilization effects of the high pressure were recognized on some strains of Saccharomyces cerevisiae, Zygosaccharomyces rouxii and food poisoning bacteria, such as Staphylococcus and Salmonella, inoculated into the jam. A taste panel indicated that the pressure-processed jam was preferred to a heat-processed jam. Pressure-processed jam and other preparations, including fruit-desserts, fruit-sauces, and fruit-dressings, and the like have been on the Japanese market since April, 1990. The essential points for pressurizing process are discussed for the future development of the newly introduced food technology. 1.

INTRODUCTION At

present, the main

field of food processing has

been

used

and

thus,

its

have

been

not the food

food

to say

including standards

processing

source

is heating.

ancient

technical

sufficiently

too much

technology

since

energy

days

basis

existing

and

the

equipments

treatment application.

basic are

on

experience,

scientific

background

Furthermore,

framework

the regulations

in the

The heating process based

and

established.

the

employed

on

food

concepts based

of

on

it

the

is

food

sanitation,

for the

designing heating

314 Heating, however, has some undesirable effects on foods themselves and the environment of the earth. Although physical and chemical changes accompanying heating are sometime desirable by giving both good cooking flavor and attractive brown color on the surface of food, heating frequently causes undesirable changes, for example, creation of unpleasant heat smell, browning of liquid appearance, and decomposition of the nutrients, thus causing a deterioration in the quality of foods. In addition, treatment at a high temperature brings about some troubles such as creation of offensive smell and the formation of some undesirable substances. In addition, the consumption of energy and the formation of carbon dioxide due to heating are serious problems these days from the standpoint of saving petroleum resources and protecting our environment. Ever since Hayashi proposed the application of highpressure food processing to solve the aforesaid problems accompanying heat treatment in 1987 (1, 2), pressurizing has attracted a great deal of scientific and industrial attention in the field of food processing (3, 4 ) . In 1990, the author and his team have developed unheated jams as marketable products processed by pressurizing for the first time in the world. In the production of jam, cooking has been employed in order to adjust flavor and improve their preservability as a processed fruit preparation. In the traditional way, fruits are heated and concentrated together with sugar and other ingredients so as to be processed into jam with high sugar concentration, or with high preservability. Jam of present days, which generally have a low sugar concentration, are put into bottles or cans after the completion of the concentration, and then sealed. Next, they are pasteurized by heating again so as to provide products which can be stored at room

315 temperature. Thus, the heating employed in the production of jams is a typical example of "well-established" methods from the viewpoint of cooking as well as improving preservability. It may be said, however, that this treatment suffers from the problems accompanying heating as such, since fading-out of the fruit's inherent color, disappearance of the delicate smell, changes in the taste and partial decomposition of vitamin C cannot be avoided. In this paper, the author would like to introduce the studies carried out with his coworkers and to discuss a pressurizing treatment applied mainly to processing fruit preparations, such as jams, while comparing it with conventional heating treatment. There have been published a number of reports and reviews on pressurizing science and technology by Hayashi as well as other workers (3-10). For a detailed reference regarding the techniques and other details described in this paper, please see report of Horie et al. related to jams (11-13) and those of Hori related to pressurizing devices (14-16). 2.

COMPARISON OF PRESSURIZING- AND HEATING PROCESSES IN JAM MAKING Fig. 1 shows a comparison of the principle of the pressurizing process developed by us and that of the conventional heating process for producing jam. The conventional method comprises the mixing of fruits, sugar and pectin under heating, concentrating the obtained mixture by heating under atmospheric or reduced pressure, putting it in bottles or cans, sealing the containers with caps, pasteurizing the products in hot water and cooling, thus giving the desired products. On the other hand, the pressurizing method consists of putting a mixture of fruits, sugar and pectin in plastic

316 Pressuri ng process

Heati ng process Fruits, sugar, pectin

Fruits, sugar, pectin 1

Mixing

Mixing

1

1

Concentration

Filling, sealing

<=Heating

1

1

Bottling, capping

Pressurization

1

1

Pasteurization

Finished product

1

Cooling I

Finished product Fig. 1. Comparison of new pressuring process with conventional process of jam preparation. containers, heat-sealing at high

pressure, thus giving

high-pressure mixture of can

the be

the containers and treating

of

treatment

fruits,

syrup

into

accelerates

sugar

and

sarcocarp.

simultaneously

the desired the

pectin

products.

gelation

and

the

Furthermore,

performed.

Thus

them

of

The the

permeation

sterilization

the

advantages

of the .pressurizing process can be fully utilized. In

practical

production,

the mixture

is exposed

to

a pressure of as high as 400 to 600 MPa at room temperature for 10 to 30 minutes. 3.

CHARACTERISTICS OF PRESSURIZING PROCESS In the pressurizing process where every step proceeds

without

heating, neither

decomposition inherent maintained

of

fresh

the

denaturaion

ingredients

flavor

while

thermal and

be observed.

color

sterilization

is

of

the

nor

Thus, the

fruit

completed.

thermal can

be

Tables

1,

2 and 3 show examples of sterilization regarding bacteria and yeasts (11) . The

quality

of

the

products

processed

by

317

TABLE 1 Effect of pressurization on food poisoning bacteria added to strawberry jam. Staphylococcus sp. 2.9 x 10 5

Initial count

Salmonella sp. 1.7 x 10 5

Coliform 7.9 x 10 5

Pressurized after allowed to stand for 24 hr at 5 °C 4.6 x 10 4 3.0 x 10 3 < 10

No treatment 200 MPa 20 min 300 MPa 20 min

< 10 < 10 < 10

< 10 < 10 < 10

Jam : 40 °Brix, pH 3.3-3.4. TABLE 2 Effect of pressuring condition and sugar concentration on survival of S. cerevisiaeOFO 0234) inoculated to strawberry jam. Sugar concentration ( °Brix) 30 40

20 Pressure — (MPa) 1 300 400 500 600

-+— — —

10 — — — —

Pressurized for, min 1 10 1 10 -H-f— — — — — —

-H-+-H — — — — —

50 1

10

-f- -+H--t-H -H -+- —

Strawberry jam : pH 3.3—3.4. Initial count : 10 5 — 10Vg. -+- : count/g >10. — : count/g <10. pressurization significantly differs from that of processed by conventional heating method. When treated by the conventional method, the inherent color tone and flavor of the original fruit are damaged and vitamin C is considerably lost. When treated by the high pressure, on the other hand, the color tone and flavor of the fruit are kept almost undamaged and vitamin C is scarcely lost. Table 4 shows examples relating to vitamin C (11). The

318

TABLE 3

Effect of pressuring condition on Z. rouxii(IFO 0505) added to strawberry jam. Pressurized at, MPa

0 10 20 10 15 10 10

0 300 300 400 400 500 600

Survival count/g

for, min (Init ial)

1.1 < < < < < <

x 10 s 10 10 10 10 10 10

Jam : 40 °Brix, pH 3.3—3.4. TABLE 4

Effect of manufacturing process on vitamin C content in pressure- and heat-processed strawberry jam. Processing stage

Mixing Fi11ing Products

Heat-processed strawberry jams Pressure-processed strawberry jam Concentrated Concentrated under under vacuum ( l ) atmospheric p r e s s u r e ( 2 ) mg/100g ( 3 ) % 39 100 37 95 37 95

mg/100g (3) % 32U) 100 26 81 25 78

mg/100g (3) % 39U) 100 29 74 28 72

(l)

5 5 °Brix. ( 2 ) 6 5 °Brix. (3) mg ascorbic acid/100g strawberry jam. Estimated value of vitamin C at the mixing s t a g e , calculated from ascorbic acid concentration in raw f r u i t and strawberry content in finished products. (4)

sensary

evaluation

on

processes mentioned here 4.

prepared

by

two

different

i s shown i n T a b l e 5 ( 1 1 ) .

PRESSURIZATION DEVICE FOR PRODUCTION OF FOOD Attempts

to

jams

develop

h a v e b e e n made o v e r pressurization

the

devices

last

c o u p l e of

applicable

to

years food

319

TABLE 5 Sensory evaluation of pressurized- and heated jam. Panelist number Sort of jam Prefered heated jam

Prefered pressurized jam

6 6 2 5 1 9 2

24 24 28 25 29 21 28

Strawberry Kiwifruit Fig Orange marmalade Grapefruit marmalade Apple White peach

processing (14-17) . In a

order

liquid

different

to

generate

should ways,

be

high

pressure,

compressed.

one

of

which

the volume

Thus,

consists

there

are

of two

of compressing

a

liquid into a high pressure container of a limited capacity (pump-pressurizing method) while another one is compressing the

capacity

of

a high

(piston-pressurizing

pressure

container with a piston

method).

Each

method

nroducts

(three

kinds

has

its

own

advantage (15). When been

sent

the to

pressurizing

first

the market method

was

ultrahigh-pressurizing Mitsubishi we

successively

MCT-150 these of

Heavy

each

employed device

Industries, changed

developed

subsequent

preparing

on April

by

studies, on

practical

scale

production

then

the

production

these

of

with

Ltd.

the

At

use

of

developed the

next

an by

steps,

the same manufacturer. we

acquired

was

jams

a

designed method

on

During

the know-how

and maintaining

experiences,

pump-pressurizing

in December, 1990.

23, 1990, the piston-

MFP-700,

jams and of operating

Based the

jam) have

the devices, namely, MCT-100 and

devices. wherein

of

was

device and

both these

for

the

assembled,

employed,

larger scale was

and

started

320 The device for practical production, which was the world's first one, is now (August, 1991) being used for production of various products, including jams, fruit-desserts, fruit-dressings and fruit-sauces· PRESSURIZING PROCESS AND PACKAGING Since water suffers from a compression loss of volume about 157o at the temperature of 20°C under a pressure of 700 MPa (14), cups (20 ml, 50 ml, 110 ml, etc.) and lids of plastics are used in our process (11). These materials have been employed by considering the following points: (1) deformable under pressure; (2) having little head space; (3) restoring after pressure deformation; (4) capable of thermally sealing; and (5) having a low oxygen permeability. Kono et al. also have pointed out similar points as the requirements for a packaging material for pressurized foods (18, 19). Since heating is never applied in the pressurizing process, no heat-resistance is required for the plastic material to be used. 5.

COMPARISON OF PRESSURIZING PROCESS WITH HEATING PROCESS 6.1 Scientific background As described above, procedures and legal regulations on the heating process have been well established. Furthermore, technological and microbiological background for the heating process has almost been established from the viewpoint of food processing. In contrast, studies on biological science under elevated pressure have just been initiated, and thus, the accumulation of experiences on the process has also been initiated just now. Therefore, the subsequent investigations should be conducted to enlarge and establish 6.

321 the background for this new process from viewpoints of wide range. 6.2 Color tone and flavor In the heating process, it is impossible to maintain the inherent color tone and flavor of fruit as such. On the other hand, the color tone and flavor of pressurized preparation are almost same with those of untreated fruit, and these features are the largest advantage of this newlyinnovated process. Furthermore, no browning is observed during the processing. These advantages are fully utilized not only in the above-mentioned jams but also in other products (for example, fruit-desserts, fruit-dressings, fruit-sauces, etc.) which have already been put on the market. On the other hand, the so-called "roasted smell" due to desirable browning such as Maillard's reaction can be obtained only by the heating process, while no such effect can be expected in the case of the pressurizing process. 6.3 Effects on microorganisms and enzymes In the pressurizing process, processed fruit food having a low pH value (for example, jam) can be sterilized commercially enough by pressurizing at room temperature. However, residual spore-forming bacteria cause a problem in a product having a high pH value. Therefore, it has been attempted to combine pressurizing with heating (20-22). It is one of important problems to be solved in future to establish sterilization of a sufficient level in the pressurizing process. We have confirmed the presence of residual enzymes in products obtained by pressurizing fruits such as kiwifruit and fig. It is desirable to suppress these enzymes by some means in order to improve the preservability of products. It is also reported by some workers that enzymes remain in other kind of pressurized

322 food products, and thus, it is a problem regarding the pressurizing process to find a countermeasure for these residual enzymes (23-25). 6.4 Energy consumption In our plant, about 0.1 1 of heavy oil is consumed for producing 1 kg of jam by conventional way. Thus, the heating process for jam-making is a typical example of heat-consuming and carbon dioxide-forming procedure. In the case of the pressurizing process, on the other hand, no direct heating is used· Furthermore, no additional energy is theoretically required after elevating pressure to a definite level. That is to say, this process is an energy-saving one. It is calculated that the energy required in the pressurizing process corresponds to 1/15 of that required in the heating process (9). 6.5 Packaging material In the case of conventional heating processes, where sterilization is performed after filling a product in the vessels, various containers, for example, metallic cans, glass bottles and plastic vessels are applicable. On the other hand, the requirements cited in the above 6.4 should satisfied in the case of the pressurizing process, which restricts available containers to those made of plastic satisfying the requirements. 6.6 Pesticide residue Although it is principally undesirable that starting materials are contaminated with pesticide residues, the residual chemicals, if any, may be thermally decomposed or vaporized during the heating steps in the heating method. Thus, the migration of the chemicals to the final product can be relieved to some extent (26, 27). However, these residual chemicals, if any, cannot be reduced in the case of the pressurizing process. Thus, attention should be paid to the contamination of starting fruits with pesticide residues.

323 In the case of application of the so-called "postharvest" chemicals, which have no chance for decreasing by decomposition or vaporization, might seriously affect the quality of the products. 6.7 Process equipments In the pressurizing process, no equipment for heating, sterilization or cooling is required. On the other hand, a pressurizing device, which is indispensable for this process, is expensive at present and its cost seems to be one of the barriers for practical application of high pressure. 6.8 Distribution system in the market Heat-processed products are generally distributed at room temperature. The quality of pressurized fruit products is damaged considerably by keeping at room temperature, because the deterioration in flavor, browning of color and softening of a gel occurs with the lapse of time due to the oxygen both remaining in the vessel and permeating through the wall of a plastic container, and enzyme remaining in the processed food. Therefore, the pressurized products should be kept and distributed at a low temperature, as pointed out for the case of orange juice (23). 6.9 Legal regulations Although there is no legal restriction in Japan on the sterilization condition in the production of jams, In JAS (28),an official standard for agricultural products, the jam is defined as a thermally processed product. Furthermore, it is described in the government regulation that a fruit juice, which is one of the fruits products, should be sterilized by heating, hence, such a regulation restricts the application of the pressurizing method to processing fruit product such as juice (29). Since no pressurizing process was known at the time when the existing legal regulation were established, it

324 seems that these regulations are to be reconsidered after the establishment of the technical and theoretical back ground for the pressurizing process. PUBLIC RESPONSES TO THE DEVELOPMENT OF PRESSURIZING PROCESS The success in the development of the pressurizing process has been repeatedly announced by the various kinds of mass media in Japan, not only immediately after the first sale of our products (April, 1990), but even now (summer, 1991). Particularly impressive responses have been obtained from farm areas and food research institutes. Under the recent severe circumstances, farm areas have been attempting to develop some special and unique product in each village to keep their economical bases. Although they have marketed various special products by processing their crops, it is very difficult to develop a fruit product keeping the inherent color and sweet smell of the fruit by the existing heating techniques. Under these circumstances, the author has had frequent inquiries for the application of this pressurizing method to the processing of agricultural products and some attempts have already been made for trial. Thus, there is a high possibility that the pressurizing process will contribute to the development in the industries in farm area, which seems a countermeasure against the liberation of the import of agricultural products. 7.

INFLUENCES BROUGHT BY DEVELOPMENT OF PRESSURIZING METHOD The author have found out, that the color and flavor of a product are directly affected by the properties of the starting fruit itself and that the difficulty in gelling varies depending on the constituents of the fruit. Therefore, the cultivation method of fruits (for example, 8.

325 fertilization) might directly affect the quality of the final products. Furthermore, this process consists of only simple procedure, and thus, it is difficult to adjust the quality of the product during the processing stage. Therefore, the agricultural materials to be used as the starting materials should be of better quality than those used in the conventional methods. Additionally, it seems necessary to develop new varieties of fruit which are suitable for this process from the viewpoints of color tone and flavor. Anyway, it is natural that this process will have a large effect on the agricultural industry since the quality of raw fruit affect directly on the quality of the final products processed by high pressure. On the other hand, the pressurization process, in which no heating is required, is a major change as described above, and one of the most effective energysaving methods. SELLING ACHIEVEMENT The total number of our products sold by the end of August, 1991, amounts to about 200,000. Subsequently, the items of the product (fruit-desserts, fruit-sauces, fruit-dressing, etc.) are successively increasing. 9.

PRESSURIZING PROCESS IN FUTURE As described above, the pressurizing process has a number of advantages. On the other hand, it has some disadvantages such that giving no roasty smell as the one obtained by heating cannot be imparted and the suppression of enzymes and sterilization effect are restricted at present. Attempts, however, have been made in order to solve these problems. Under the recent diversification in eating habits, 10.

326 the prospect of pressurized products, which have a fresh flavor and a good preservability, seems to be bright. It seems possible to prepare semi-cooked foods and novel food products, which have never been seen so far. Based on our practical experiences, the author would like to point out that further studies are required in order to clarify the pressure-resistance levels of microorganisms, monitor the behaviors of various enzymes under elevated pressure and examine the properties of proteins and starches under high pressure. These subjects should be highly interesting from the scientific viewpoint. Accordingly, it may be pointed out that the attainment of following reservations are required for the further development of the pressurizing process in future. Theories, information and experiences should be further accumulated and systematically organized from both scientific and practical points of view. High pressure devices would be improved and standardized based on repeated experiences and practice, and thus, become less expensive. The types and varieties of pressurized food product would increase and be enlarged in amount, and thus these foods would be commonly recognized as a group of processed foods regarding their handling in the market and evaluation for taste. Pressurized food products would be more widely accepted, and thus, handled as a certain types of food in relation to the laws, regulations and official standards. 11.

CONCLUSION This is just the first time for the author and his team to process pressurized foods, and over the last year, the new products have been tasted by many consumers already. In this inexperienced field, the author is now

327 faced with new problem one after another, in addition to improving the degree of completion of this novel process. It is believed that the realization of the pressurized food products will give stimulation to the food industry as well as the processing machinery industry. It will give us great pleasure too if our technology would contribute to the development of the pressurizing process in future. REFERENCES 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

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328

17 18 19 20

21 22 23

24 25

26 27 28 29

pp. 351-369 (in Japanese). T. Kanda, in: R. Hayashi (Ed.), Pressure-Processed Food—Research and Development, San-ei, Kyoto, 1990 pp. 341-350 (in Japanese). M. Kono, Shokuhin To Kaihatsu, Vol. 24, No. 12 (1989) pp. 68-72. M. Kono and Y. Nakagawa, in: R. Hayashi (Ed.), Pressure-Processed Food—Research and Development, San-ei, Kyoto, 1990, pp. 303-313 (in Japanese). Y. Taki, T. Awao, N. Mitsuura, Y. Takagaki, in: R. Hayashi (Ed.), Pressure-Processed Food—Research and Development, San-ei, Kyoto, 1990, pp. 143-155 (in Japanese). N. Mitsuura, Shokuhin To Kaihatsu, Vol. 24, No. 12 (1989) pp.62-67. T. Awao and Y. Taki, Kagaku Kougaku, Vol. 54, No. 4 (1990) pp.283-285. H. Ogawa, K. Fukuhisa, K. Sasai, Y. Kubo, H. Fukumoto, in: R. Hayashi(Ed.), Pressure-Processed Food—Research and Development, San-ei, Kyoto, 1990, pp. 179-191 (in Japanese). Y. Ifuku and Y. Takahashi, in: R. Hayashi (Ed.), Pressure-Processed Food—Research and Development, San-ei, Kyoto, 1990, pp. 165-177 (in Japanese). A. Hara, G. Nagahama, A. Ohbayashi, R. Hayashi, in: R. Hayashi (Ed.), Pressure-Processed Food—Research and Development, San-ei, Kyoto, 1990, pp. 225-234 (in Japanese). S. Ishikura, S. Onodera, S. Sumiyashiki, T. Kasahara, M. Nakayama, S. Watanabe, J. Food Hyg. Soc. Japan, Vol. 25, No. 2 (1984) 203-208. H. Sekida, K. Sasaki, Y. Kono, A. Takeda, M. Utiyama, Eisei Shikenjo Houkoku, 103 (1985) pp. 127-129. The Japanese Agricultural Standards, 1990. Food Sanitation Low, issued by Ministry of Health and Welfare, Japanese Gavernment, 1988.