METHODS OF FOOD PROCESSING FOR STORAGE
METHODS OF FOOD PROCESSING FOR STORAGE
Jasur Safarov
DSc, professor Tashkent State Technical University,
Uzbekistan, Tashkent
Shakhnoza Sultanova
DSc, professor Tashkent State Technical University,
Uzbekistan, Tashkent
Ulugbek Khujakulov
researcher Tashkent State Technical University,
Uzbekistan, Tashkent
The goal of food technologists was to increase the shelf life of fresh products. Until recently, research has mostly focused on extending the shelf life of whole fruits and vegetables. The new challenge is to expand and expand the knowledge of minimally processed fruits and vegetables. The production of minimally processed foods will grow rapidly in the coming years if new methods are developed to extend shelf life while ensuring food safety. The development of these new technologies for the production and sale of ready-to-eat fruits and vegetables is a challenge for the food industry.
As mentioned in the previous section, extending the shelf life of minimally processed fruits and vegetables faces two main challenges. First, plant tissue is a living, breathing tissue in which many chemical reactions interact. Some reactions, if left unchecked, can lead to rapid aging or change in quality. Second, microbial growth must be slowed down. The growth of pathogens raises food safety concerns, especially higher pH vegetables compared to lower pH fruits. Visible growth or odor caused by microorganisms is aesthetically unacceptable.
Numerous technical barriers must be overcome to address these challenges. Control of plant tissue physiology and microbiological growth is critical for minimally processed fruits and vegetables. The tissue must remain alive and maintain quality for a reasonable shelf life. Packaging should also be designed to help achieve these goals. Distribution must meet the requirements that will necessarily be required to present these products to the consumer.
Canning methods for extending the shelf life of minimally processed vegetables can use many of the classic food preservation procedures. These methods can be: cooling; chemical treatment with acidifiers, antioxidants or antimicrobials; modified atmosphere packaging.
In some cases, reducing water activity (aw) by removing moisture can seriously reduce the turgor and fresh appearance of minimally processed vegetables. On the other hand, if a decrease in aw produced by the addition of osmotic agents such as sugar or salt, the resulting product may have an undesirable taste and aroma different from that of fresh vegetables.
Freezing storage usually results in a change in the texture and other characteristics of fresh vegetables.
Required Heat Treatment to Kill Listeria monocytogenes, numerous Salmonella species and elimination of C. botulinum toxin production may impair the preservation of taste, aroma, texture, color and nutritional value of fresh vegetables.
Treatment with ionizing radiation (irradiation) is often suggested as a means of extending the shelf life of fresh fruits and vegetables. Unfortunately, the levels of radiation needed to prevent microbiological spoilage cause tissue softening.
Refrigerator storage. Refrigeration above freezing during distribution and sale is a necessary step for minimally processed vegetables. Cool temperatures slow down the rate of microbiological growth and effectively reduce enzyme activity. Most of the metabolic reactions of pathogenic microorganisms and phytopathogens are catalyzed by enzymes. The importance of enzyme activity in minimally processed vegetables makes refrigeration absolutely necessary for these foods. The rate of enzyme-catalyzed reactions is highly dependent on temperature. For every 10 °C temperature increase (in the biological range) the reaction rate increases by 2-4 times. This is known as the temperature coefficient Q1. Conversely, a decrease in temperature for every 10 °C leads to a similar decrease in the rate of biological activity. The low temperature is effective in slowing down the metabolic rate and thus delaying tissue destruction. This indicates that refrigeration should be a constant factor in preserving minimally processed vegetables.
Lowering the temperature reduces the rate of respiration and slows down aging. At temperatures above 10 °C CO2 production increases markedly due to increased metabolism and microbial growth.
Lowering the temperature reduces the development of unpleasant odors peas and loss of hardness in tuber slices. It also reduces discoloration in damaged tissues by reducing the activity of the enzymes tyrosinase and o-diphenyl oxidase. The loss of green color in chopped lettuce is much less at 2 °С than at 10 °C. The loss of vitamin C in spinach is reduced from 79% to 33% when the storage temperature is reduced from 20°C to 4°C.
At the same time, lowering the storage temperature makes it possible to reduce the growth of the microflora of ready-to-eat vegetables. Lowering the temperature effectively increases the dead time and reduces the rate of reproduction or generation time of microorganisms. The population of mesophilic microorganisms in samples of minimally processed cabbage after 10 days of storage at 4 °C was 100-1000 times lower than the populations observed in samples stored at 12 °С and 20 °C.
But microorganisms react differently to lower storage temperatures. In leafy vegetables stored at low temperatures, the flora is formed mainly by gram-negative bacteria, and when the temperature rises, the flora changes to lactic acid-producing gram-positive bacteria.
In the past, 6 °C was considered safe to prevent the growth of pathogenic bacteria. However, with the advent of minimally processed foods with extended shelf life, special attention should be paid to microorganisms that thrive at temperatures below 6 °C, such as C. botulinum type E and non-proteolytic B and F strains, V. parahaemolyticus strains and Y. enterocolitica.
Another foodborne disease is caused by L. monocytogenes, a facultative anaerobe that can survive and reproduce at temperatures from 1 °С up to 45 °С with an optimal growth temperature of 30-37 °C and has become one of the main safety issues in minimally processed vegetables, as it can develop at temperatures close to 0 °C and down to -1.5 °C.
The main problem associated with minimally processed fruits and vegetables is the possibility of temperature disturbance during distribution, transportation, storage or sale. Fruits and vegetables are generally classified as long shelf life products and, in the best conditions, they should have time/temperature indicators that alert both consumers and processors when temperatures are exceeded.
Chemical processing. Chemical treatments used natural or synthetic chemicals to control spoilage and maintain product quality. There are antimicrobial compounds and antioxidants that prevent browning, discolouration of the pigment and protect against loss of taste and aroma, change in texture and loss of nutritional qualities.
The action of an antimicrobial compound depends on the type, genus and type of microorganism. The effectiveness of an antimicrobial also depends to a large extent on other factors such as pH, water activity, temperature, gas atmosphere, initial microbial load, and type of food.
The effectiveness of compounds acting as antioxidants depends on many factors: pH, water activity, temperature, light, type and activity of the enzymatic system, gas atmosphere, type of food, heavy metal content. The effectiveness of antioxidants is controlled by the environmental conditions of the food system, their concentration and persistence during storage or shelf life of the product.
In minimally processed vegetables, the use of both antimicrobial and antioxidant compounds should be considered to ensure a safe or harmless high quality fresh product throughout its useful life. This suggests that conservation barriers used for minimally processed vegetables must act both on microbial flora load and on key enzymes that can cause quality issues.
Organic acids, naturally present in foods, accumulated from fermentation, or intentionally added during processing, have been used for years to combat microbiological spoilage. Some organic acids act primarily as fungicides or fungistatics, while others tend to be more effective in inhibiting bacterial growth. Current evidence suggests that the mode of action of organic acids is due to a direct decrease in the pH of the substrate, a decrease in intracellular pH due to ionization of an undissociated acid molecule, or a disruption in the mechanism of transport across the cell membrane.
Since the non-dissociated form of the acid molecule is primarily responsible for antimicrobial activity, the effectiveness depends on the dissociation constant (pKa) of the acid. Since the pKa of most organic acids is between 3 and 5, organic acids are generally more effective at low pH values. Thus, acidification of low acid foods significantly improves the antimicrobial characteristics of the food. However, this mechanism depends on the complete diffusion of the acid through the sample and into the center of each food particle involved in acidification.
Numerous organic acids have been used as antimicrobial agents in various types of foods: citric, succinic, malic, tartaric, acetic, sorbic, benzoic, lactic, and propionic acids, among others. The effect of citric acid on microbiological development is detailed below. Citric acid is a compound that occurs naturally in fruits and vegetables and is considered GRAS (Generally Recognized as Safe); When used in adequate concentrations, it does not adversely affect the organoleptic, nutritional, and safety characteristics of the fresh vegetable, and is recommended for use in minimally processed vegetables by many authors.
References:
- King A.D., Bolin H.R. Physiological and microbiological stability during storage of minimally processed fruits and vegetables. Food Technol. 2016, 43(2), 132-135/139.
- Feasting Meng, Guemes D.R., Piagentini A.M., Di Pentima J.H. Storage quality of minimally processed cabbage in plastic wrap. J. Food Quality, 2020, 20(5), 381-389.