10 Food Preservation Technology -...

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Food Preservation Technology

10 Food Preservation Technology10.1 Food Preservation

10.1.1 Why is Food Preservation Important?

10.1.2 Principles of Food Preservation

10.1.3 Methods of Food Preservation

10.1.4 Are Preservatives Safe?

10.2 Food Packaging

10.3 Nutrition Labelling

10.3.1 Why is the Nutrition Labelling Scheme needed?

10.3.2 What is in the Scheme?

10.3.3 Are nutrition labels on all prepackaged food?

10.4 How to read a Nutrition Label?

Contents Page

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10 Food Preservation Technology10.1 Food PreservationFood is a perishable commodity. The primary objective of food preservation is to prevent or slow down the growth of micro-organisms including moulds, yeasts and bacteria as the growth of these micro-organisms causes spoilage of food.

10.1.1 Why is Food Preservation Important? (A) To increase the shelf life of food as well as its supply. Although the freshness,

palatability and nutritive value may be altered with time delay, perishable foods can be preserved to prevent spoilage and made to be available throughout the year. In this way, preservation helps to increase variety in our diet and makes it better balanced.

(B) To save food for future use at the time of scarcity or drought etc. after suitable preservation and proper storage. Preservation of food also minimises the preparation time and energy at home.

(C) To stabilise the price of food throughout the year since seasonal food can be preserved and made available for consumption throughout the year.

10.1.2 Principles of Food Preservation (A) Prevention or delay of the growth of micro-organisms(i) Avoiding invasion of micro-organisms e.g. by aseptic techniques(ii) Removing micro-organisms e.g. filtration(iii) Inhibiting the growth and activity of micro-organisms e.g. freezing, refrigeration, drying, anaerobic conditions, chemicals or antibiotics(iv) Killing the micro-organisms e.g. heat or irradiation

(B) Prevention or delay of self-decomposition(i) Destruction or inactivation of inherent enzymes naturally existing in food e.g. by blanching(ii) Prevention or delay of chemical reactions e.g. prevention of oxidation by using antioxidants

(C) Prevention of damage from insects or animals(i) By using suitable chemicals to kill insects or animals from destroying the foods.(ii) By storing foods in dry, air tight containers to prevent the insects or animals from destroying them.

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Food preservation methods

Inhibition Inactivation Avoid recontamination

Low-temperature storageReduction of water activityDecrease of oxygenIncrease of carbon dioxideAcidificationFermentationAdding preservativesAdding antioxidantsControl pHFreezingDryingConcentrationSurface coatingStructural modificationsChemical modificationsGas removalChanges in phase transitionHurdle technology

SterilisationPasteurisationIrradiationElectrifyingPressure treatmentBlanchingCookingFryingExtrusionLightSoundMagnetic field

PackagingHygienic processingHygienic storageAseptic processingHACCPGMPISO 9000TQMRisk analysis and management

10.1.3 Methods of Food Preservation(A) AsepsisAsepsis is the absence of micro-organisms. Packaging prevents the entry of micro-organisms into food.

(B) FiltrationFiltration can successfully remove micro-organisms from water, fruit juice, beer, soft drinks, wines, etc. This method is used for liquid only. The liquid is filtered through a sterilised filter by applying pressure. Micro-organisms in the liquid cannot pass through the filter and may stay on one side while the liquid without micro-organisms will pass to another side of the filter.

Figure 10.1 Major Food Preservation Techniques

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(C) Anaerobic conditionAnaerobic condition means a condition lack of or containing only minimum amount of air or oxygen. It can prevent the surviving bacteria in food from growing in the container. The container is completely filled with food and air in unfilled space is removed or replaced by nitrogen or carbon dioxide.

(D) Heat treatmentHeat is the most commonly used media for preservation by killing micro-organisms. The heat treatment required depends on the kind of the target micro-organisms to be killed and the composition of the food. Basically, heat treatment can be classified into three categories:

(i) Pasteurisation (temperature below 100℃)Pasteurisation is a heat treatment that kills part of the micro-organisms present in food using a temperature under 100℃. The temperature used ranges from 65-75℃. There are two ways of pasteurisation:

❖ HTST (High temperature-short time) Food product is heated at high temperature for a short time. For example, milk is heated to 72℃ and held for 15 seconds.

❖ LTLH (Low temperature-long time) Food product is heated at a lower temperature for longer period of time. For example, milk is heated to 62.8℃ and held for 30 minutes.

(ii) Boiling or heating at about 100℃Most fruits and vegetables can be preserved for a longer time by applying heat at about 100℃. Inherent enzymes which initiate self-decomposition can be destroyed after boiling at 100℃. This process is called blanching.

(iii) Sterilisation (temperature 100℃ or above)It is a process that all micro-organisms are being killed at high temperature or radiation. The time and temperature necessary for sterilisation vary with the type of food. For example,

Type of food

Fruit and tomato

Vegetables

Milk(ultraHeat

Treatment(UHT))

Temperature

100℃

116℃135℃

Duration

30 minutes

30-70 minutes

not lessthen 1 second

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(iv) CanningCanning is a process in which over 100℃ is used for killing all spoilage organisms and their spores as well as inactivating enzymes and sealing in sterile airtight containers. The packaging materials for canning can be tin or glass.

(E) Use of low temperature and cold preservationLow temperature can lower the rate of chemical reactions and the action of enzymes. Generally, freezing can prevent the growth of most food-borne micro-organisms and the usual temperature for cold storage is 4.5-7℃. Refrigeration temperature lowers the growth rate of micro-organisms and chilling can slow down the enzymatic and microbial changes in food. For frozen food, it should be stored at or below -18℃ where the enzymatic and microbial changes may be stopped or extremely slow.

(F) Drying or dehydrationFoods are preserved by drying for a long history, especially in Chinese foods. Mushrooms, dried shrimps and salted fish are some typical examples. Both the terms “drying” and “dehydration” mean the removal of water. “Drying” usually describes the process of drying under sunshine or open air. The other term, dehydration, usually describes the removal of moisture by applying artificial heat current under controlled conditions.

Function

Temperature

Advantage

Disadvantage

Pasteurisation

Partial destruction of micro-organisms

Temperature below 100℃

Minimal damage to flavor, texture, and nutritional quality

Short shelf life. Another preservation method must be used, such as refrigeration or freezing

Sterilisation

Complete destruction of micro-organisms

Temperature 100℃ and above

Long shelf life. No other preservation method is necessary

Food is overcooked. Major changes in texture, flavor, and nutritional quality

Table 10.2 Major differences between pasteurisation and sterilisation

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Dehydration

A faster process

Under controlled hygienic conditions

Not dependent on the weather

Investment on mach inery and processing cost is needed

Sun-drying

A slower process

Under open-a i r condi t ions wi th l i t t le hygienic control

Not possible in cloudy weather or rainy days

No machinery and processing cost is needed

(G) Use of preservativesPreservatives serve as antimicrobials which prevent or slow down the growth of moulds, yeasts and bacteria. By preventing the growth of moulds, yeasts and bacteria, preservatives can improve the safety of food as well as prevent the wastage of seasonal surplus by making it last longer on the shelf or in the fridge. An ideal preservative should meet the following criteria:

(i) can inhibit the growth of a wide range of micro-organisms

(ii) should be non-toxic to humans

(iii) should not be expensive

(iv) should not affect the flavour, taste or aroma of the food product

(v) should not be inactivated by the food itself

(vi) should not promote the development of resistant micro-organisms

(vii) should kill rather than inhibit the micro-organisms

Table 10.3 Comparison of dehydration and sun-drying

Table 10.4 Some common preservatives

Preservatives

Sulfites

Sodium nitrate

Propionic acid

Sorbic acid

Benzoic acid

Target Organism(s)

Yeasts and bacteria

Bacteria

Moulds

Moulds

Yeasts and moulds

Action

Antioxidant

Antimicrobial

Antimicrobial

Antimicrobial

Antimicrobial

Examples of Application(s) in Food

Dehydrated fruits and vegetables, wine, juice, sausages

Cured meats

Bread, cakes, cheese

Cheeses, cakes, salad dressing, wines

Soft drinks, ketchup, salad dressings

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Table 10.5 Maximum limits of the commonly used preservatives listed in Hong Kong Food law

Chemicals

Sulfites

Sodium nitrate

Propionic acid

Sorbic acid

Benzoic acid

Specific food

Cabbage, dehydratedCiderCoffee extract, solidFruit juicesWine

BaconHamMeat, pickledPork, preserved

Bread

CheeseSalad dressing

Soft drinksSalad dressingKetchup

Maximum parts per million (ppm)

2500200150350450

500200200200

3000

10001000

160250300

(Adapted from Part V (Food and Drugs) of the Public Health and Municipal Services Ordinance (Cap. 132))

(H) Use of salt and sugarSugar binds moisture and thus can preserve food by preventing the growth of micro-organisms if a high concentration (65% or above) is used. Products such as jams and jellies are preserved by using sugar.

Salt in high concentration (15-20%) can prevent the water from being available for bacterial growth. It can slow down the growth rate of bacteria and thus the food is preserved. Salt can be used in brine (salt water) or applied to food directly.

(I) Use of acids (vinegar or citric acid)Acids lower the pH and thus inhibit the growth of many micro-organisms. It is more effective against yeast and bacteria than moulds. About 20% vinegar (acetic acid) prevents the spoilage of most products. It is used in the preservation of pickles, sauces and chutney. Another acid, citric acid, is also used in the preservation of certain fruits and vegetables. Products of jams, jellies and squashes may contain citric acid. It lowers the pH of the food products and can prevent the growth of moulds.

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Table 10.6 Examples of acidulants used in the food processing industry

Acid

Acetic

Benzoic

Citric

Lactic

Malic

Phosphoric

Propionic

Tartaric

Comment

Provides flavour, decreases pHSodium acetate is salt form present in vinegar

As sodium benzoate, effective antimicrobial agentOccurs naturally in cranberries

Provides flavour, decreases pH, acts as chelating and sequestering agentOccurs naturally in citrus fruits

Provides tartness

Provides flavourOccurs naturally in apples

Provides flavour and tartness in beveragesEnhances juiciness in meats (as phosphate)

As calcium propionate, effective antimicrobial agentProduced in some cheeses

Present in baking powder as potassium tartrate saltOccurs naturally in grapes

(J) IrradiationFood absorbs and is heated up by radiant energies. Radiant energies can kill micro-organisms without marked increase of temperature as well as marked changes in the nature of food. Gamma rays, x-rays and electromagnetic, ultra-violet radiations are commonly used for food preservation. Irradiation can be used in a wide range of area in food preservation:

(i) Poultry products and seafood

(ii) Fruits

(iii) Prevention of sprouting in potatoes and onions

(iv) Delaying ripening in fruits

(v) Preservation of seafood

(vi) Prevention of insect infestation in dry foods and food products

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Table 10.7 Applications of food irradiation

Application

Sterilisation

Sterilisation of packaging materials

Destruction of pathogens

Control of moulds

Extension of chill life from 5 days to 1 month

Inactivation/control of parasites

Disinfestation

Inhibition of sprouting

Dose range(kGy)

7-10

Up to 50

10-25

2.5-10

2-5

2-5

0.1-6

0.1-2

0.1-0.2

Examples of foods

Herbs, spices

Long term ambient storage of meat (outside permitted dose)

Wine corks

Spices, frozen poultry, meat, shrimps

Extended storage of fresh fruit

Soft fruit, fresh fish and meat at 0-4℃

Pork

Fruit, grain, flour, cocoa beans, dry foods

Potatoes, garlic, onions

Countries with commercial processing

Belgium, Canada, Croatia, Czech Republic, Denmark, Finland, Israel, Korea(Rep.), Mexico, South Africa, USA, Vietnam

None

Hungary

Belgium, Canada, Croatia, Czech Republic, Denmark, Finland, France, Iran, Netherlands, South Africa, Thailand, Vietnam

China, South Africa, USA

China, France, Netherlands, South Africa, USA

--

Argentina, Brazil, Chile, China

Algeria, Bangladesh, China, Cuba

10.1.4 Are Preservatives Safe? All preservatives must go through rigorous safety assessment and approval procedures. They are permitted for food use only when they are proved to present no hazard to the health at the level of use proposed.

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Although many allergic reactions to foods are caused by natural food ingredients such as milk, fish and peanuts, some are caused by food additives such as sulphur dioxide. Sulphur dioxide is used as preservative in a wide range of foods, in particular soft drinks, sausages, dried fruits and vegetables. Sulphur dioxide, benzoic acid and sorbic acid all have long history of safe use. They are generally of low acute and chronic toxic effects, and should not pose significant health effect to consumers upon normal consumption of the preserved fruits and vegetables concerned.

Nitrite is mainly used in sausages, ham, bacon and pickled meat to inhibit the growth of Clostridium botulinum. Accidental intake of large amount of nitrite can cause a kind of blood disorder called methaemoglobinaemia. Ingested nitrite, in the presence of protein substances in the stomach, may form N-nitroso compounds, which have been shown to be probable human carcinogen and may increase the risk of stomach cancer. Nitrite also occurs naturally in food like cereals and vegetables.

If consumers have balanced diets, exposure to a specific chemical will be lowered and so is the risk.

10.2 Food Packaging

Commercially sterile foods are processed and packaged in a manner that leaves the food free of micro-organisms of public health significance, and prevents the growth of any microorganism under normal non-refrigerated storage condition and distribution. This may be accomplished by aseptic processing and packaging.

Aseptic processing and packaging refers to a technique in which food is commercially sterilised outside the package, cooled and aseptically filled in a previously sterilised package, followed by hermetical sealing with a sterilised closure in an atmosphere free from micro-organisms. The end product is a hermetically sealed container holding sterile food, which can be stored for prolonged periods of time at ambient conditions.

According to the acidity, foods may be divided into low-acid foods and acid foods. Low-acid food means any food, other than alcoholic beverages, where any component has a pH value greater than 4.6 after heat processing. These foods are considered perishable as pH above 4.6 may support growth of food spoilage or poisoning micro-organisms such as Clostridium botulinum. A good manufacturing practice is essential to ensure the safety and quality of these food products.

Aseptic processing and packaging of low-acid foods is a complex food manufacturing operation. It requires careful control at all stages of production to produce and maintain the asepsis of the food processing, filling and packaging systems. The control system embraces a large number of operations which are inter-related.

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10.3 Nutrition Labelling

Nutrition information on food labels is an important public health tool to promote a balanced diet, hence enhancing public health. This information assists consumers to better understand the nutritional value of food. It enables consumers to compare the nutritional values of similar food products and then make healthy food choices based on the relevant nutrition information. For those who are on special diets (e.g. people suffering from diabetes or high blood lipid), nutrition information on food labels enables them to select suitable food and help manage their conditions.

The Food and Drugs (Composition and Labelling) (Amendment: Requirements for Nutrition Labelling and Nutrition Claim) Regulation 2008 (the “Amendment Regulation”), enacted by the Legislative Council on 28 May 2008, came into force on 1 July 2010. The Amendment Regulation introduces a Nutrition Labelling Scheme which covers two types of nutrition information on food labels, namely nutrition labelling and nutrition claims. The Scheme requires that nutrition labels setting out the content levels of energy and seven nutrients specified for labelling (namely protein, carbohydrates, total fat, saturated fat, trans fat, sodium and sugars) will become mandatory for all applicable prepackaged food products. In addition, nutrition claims made on food labels or in advertisements of prepackaged food products will also be regulated. Manufacturers can only use nutrition claims if their products meet specified conditions.

10.3.1 Why is the Nutrition Labelling Scheme needed?

(A) A Nutrition Labelling Scheme (the Scheme) aims to assist consumers:(i) to make informed food choices(ii) to encourage food manufacturers to apply sound nutrition principles in the formulation of foods(iii) to regulate misleading or deceptive labels and claims.

(B) Consumers can use the information on the nutrition label in many ways:(i) to compare nutritional content among different foods for a healthier choice, e.g. to choose food lower in fat, sodium (or salt) and sugars.(ii) to understand the nutritional content of food and estimate their contribution to the overall diet.(iii) to meet individual’s dietary needs.

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10.3.2 What is in the Scheme?Both nutrition labels and nutrition claims are included in the Scheme; these two elements serve two different purposes. Nutrition labels provide consumers with information on energy and nutrient values of the food so that they can make use of the information to choose foods that are good for their health. Setting conditions for nutrition claims standardise the meaning of various claims so that consumers can know the real meaning behind each claim. For example, when they see a claim of “low sugars”, they can know that the product should contain not more than 5 g of sugars per 100 g/mL of the food.

(A) Nutrition Labels(i) Nutrition label is a systematic way of presenting nutrition information of food products. It is usually in a tabular format with a heading like “Nutrit ion Information”, “Nutrition Facts” or “Nutrition Label”.(ii) Once the Scheme is enforced, consumers can find “1+7” items (i.e. the values of energy plus seven specified nutrients-protein, total fat, saturated fat, trans fat, carbohydrates, sugars and sodium) on the nutrition labels.

(B) Nutrition Claims(i) Generally, claims are eye-catching descriptors found on food packages. They can serve as a quick reference for selected nutrition information. They may highlight the content of certain nutrients (e.g. low fat, high fibre, etc.), or tell you how the nutritional content of a particular food product differs from another similar food (e.g lower cholesterol), or describe the physiological function of a nutrient which is present in the food (e.g. calcium builds strong bones). These nutrition claims will be regulated from 1st July 2010 and they must meet certain specified conditions before making the claims.

(ii) There are 3 main types of nutrition claims:

❖ Nutrient content claim is related to the contents of nutrients found in food. It describes the level of a nutrient contained in a food, such as, “High calcium”, “Low fat” and “Sugars free”. Overall speaking, there are five categories of nutrient content claims namely “Free” claim, “Very low” claim, “Low” claim, “Source” claim and “High” claim. Words with similar meaning may be used as well.

❖ Nutrient comparative claim is also related to the contents of nutrients found in the food. Rather than describing the nutrient level, nutrient comparative claim compares the nutrient levels of two or more similar food products, such as “Reduced fat-25% less than the regular product of the same brand”. Similar to nutrient content claims, wordings with similar meaning may be used.

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For detailed conditions, please refer to the Amendment Regulation and Technical Guidance Notes on Nutrition Labelling and Nutrition Claims: http://www.cfs.gov.hk/english/food_leg/food_leg_nl_guidance.h tml

❖ Nutrient function claim describes the physiological role of a nutrient in growth, development and normal functions of the body (e.g. “Calcium builds strong bones.”). It must fulfil several general principles, such as the claim must be supported by science and the information about the physiological role of the claimed nutrient must be included in the claim. Nutrient function claims that are commonly used, such as “Protein helps build and repair body tissues” and “Iron is a factor in red blood cell formation”, can be found on the webpage of the Centre for Food Safety: http://www.cfs.gov.hk/english/food_leg/files/Acceptable_Nutrient_Function_ Claims_bilingual.pdf

(iii) Nutrition claims should be used as a quick reference only. The content value of the claimed nutrient can be found on the nutrition label. At any time, consumers should not focus only on the claimed nutrients. Consumers are advised to refer to the nutrition label for detailed information on the overall nutritional property of the food product for making healthy food choices.

(iv) For instance, although a product with a “low sugars” claim should have a low enough sugars content in order to bear such claim, consumers should refer to the nutrition label to ascertain that the product does not have high contents of fat or energy, particularly if he/she is interested in weight maintenance. In addition, a product with a “sugars free” claim does not necessarily mean that it is free of carbohydrates. Consumers, particularly diabetic patients, should refer to the nutrition label to verify the carbohydrates content of the product.

10.3.3 Are nutrition labels on all prepackaged food?Majority of the prepackaged food will have nutrition labels after 1st July 2010. However, some products are exempted from the requirements due to various reasons. For example, there may be practical difficulties for providing nutrition labels in very small packages (e.g. a container with a total surface area of less than 100 cm2). Food, such as tea leaves, spices and distilled water, which contain insignificant amount (nearly zero) of energy and specified nutrients, as well as raw meat, fresh fruits and vegetables without any addition of ingredients are also exempted from the nutrition labelling requirements.

Furthermore, prepackaged food products with annual sales volume of 30,000 units or below may also apply for exemption from the requirements of nutrition labelling. Products exempted due to low volume of sales will have stickers on the packages to indicate their exemption status. Such stickers may be in circular, square or rectangular shapes. Sometimes, an exemption number may be found on the stickers as well.

For imported foods, they are also required to follow the labelling scheme. On the other hand, the format of the original label is as the Nutrition Facts Panel which is under the Federal Food Drug and Cosmetic, the USA. Food labelling is required for most

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prepared foods, nutritional labelling for raw produce (fruits and vegetables) and fish is on a voluntary basis. The nutritional information should be labelled as the Nutrition Facts Panel format.

Under the proposal, nutritional labels must conform to a particular way for expressing the nutrient content, the basic format is to express the energy or nutrient content in absolute amount in kilocalories/metric unit per 100g of food but not as Nutrition Facts Panel format. In addition, nutritional labels should be displayed conspicuously on the package. At present, there is no plan to regulate the format of the labels other than those expressing the nutrient contents.

Figure 10.8 Example of a nutritional label proposed to be used in Hong Kong in 2010.

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① Serving SizeTo read a nutritional label, first we should identify the serving size and the number of servings appeared on the package. Serving sizes are standardised to make it easier to compare similar foods with familiar units, such as cups or pieces, and followed by the metric amount like the number of grams.

② Calories (and Calories from Fat)Calories provide a measure of how much energy is obtained from a serving of food. The unit should be in Kcal or C.

③ Limit these nutrientsNutrients including fat, cholesterol and sodium should be limited in their intake and eaten in adequate amounts.

④ Get Enough of these NutrientsGet enough dietary fibre, Vitamin A, Vitamin C, calcium, and iron in every diet.

10.4 How to read a Nutrition Label?

① Start Here

② Check Calories

③ Limit these Nutrients

④ Get Enough of these Nutrients

⑤ Footnote

⑥ Quick Guide to % DV

．5% or less is Low

．20% or more is High

Sample label for Macaroni & Cheese

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⑤ FootnoteThe footnote in the lower part of the nutritional label indicates the statement: “% DVs is based on a 2,000 calorie diet” on all food labels. But the remaining information in the full footnote can be exempted if the size of the label is too small. The footnote should be the same and should not be different from product to product.

⑥ The Percent Daily Value (%DV): The % Daily Values (%DVs) is based on the Daily Value recommendations for key nutrients but only for a 2,000 calories daily diet. The %DV indicates whether a serving of food is high or low in a particular nutrient. This allows consumers to compare different brands and also to distinguish nutrition claim of particular nutrients such as reduced fat, or low fat by using this %DV.

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Not for SaleThe copyright of the materials in this booklet belongs to the Education Bureau. The materials can be used by schools only for educational purpose. Written prior permission of the Education Bureau must be sought for other commercial uses.

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