Institute of Technology of Cambodia Department of Chemical Engineering and Food Technology Food Spoilage and Food preservation Professor : Dr. Hul Seingheng Group member:I3GCA-3 Hun Lina Huot Syradeth Kak Mei Khuon Chann M. Kin Kimsok 2010-2011

II. How can food be preserved? I. How do microbes cause food spoilage? II. How can food be preserved? Physical method Chemical method

Food spoilage is the process which damage the food Spoiled food is the food whose chemical characteristic is destroyed, and it is smelly, bad appearance, the unpalatable taste, odour or texture. Why the food are spoiled? Microbes, chemical reactions food spoilage

Chemical reaction: oxidation, enzymatic activity Microbes break down Protein into amino acid, amines, hydrogen sulphide and amonia. . Hydrogen sulphide smelly . Sulphur smelly . Fats . Carbohydrate acid, alcohol, gas Chemical reaction: oxidation, enzymatic activity

Microbes that cause food spoilage called Proteolytic. They are Enterobacteriaceae, staphylococci, micrococci, aerobic Gram-positive sporing bacilli, pseudomonads, moulds… For example: Black spots on meat are caused by Cladosporium species. White spots are caused by Sporotrichum carnis. Yellow or green are caused by Penicillium species.

Milk is an excellent growth medium for bacteria, moulds, yeasts. -Souring of milk is the result of acid fermentation by lactobacilli ( or lacto bacteria or Clostridium septicum). -Clostridium sordelii is a clostridium that causes milk proteins to clot

-Lactococcus cremoris and Enterobacter aerogenes causes the formation of ‘ropy’ milk. -Clostridium sporogenes break down milk proteins to produce alkaline products. -Clostridium novyi forms gas from milk. In turn, moulds and yeasts may break this down.

II. How can food be preserved? Physical method Pasteurize Sterile Cooking Chilling Drying Osmotic protection Filtration Irradiation Vacuum package 2. Chemical method

1. Physical method Pasteurize The process that slow the activities of microbes Condition: ~ 60 0C -70 0C for 15min b. Sterile The process that almost completely kills microbes Condition: >121 0C for about 5min c. Cooking This process causes the denaturation of autolytic enzymes, tenderises food, imparts desirable flavours and odours to the food and it alters the microbial flora, eliminating many heat-sensitive organisms. Cooking does not always kill microorganisms.

Overcooking may produce an unacceptable food. There may be a conflict between a desirable food and one that is microbiologically safe. The soft-boiled egg affords a good example of cooking. d. Chilling is used to delay its decomposition, to slow the growth of spoilage organisms and to retard the activities of autolytic emzymes by storing food in the low temperature (the refrigerater).

However, it is not without problems: Listeria monocytogenes grow very well at the temperatures found in refrigerators. -cook-chill food : at the temperature above freezing -strawberies: not suitable for freezing (flash freezing) e. Drying The process of removing the water from the food. NB: Dried fruits and vegetable often retain some water that moulds can grow .

Two principal processes: salting or high sugar environment. f. Osmotic protection Two principal processes: salting or high sugar environment. Most spoilage bacteria and yeasts cannot tolerate salt concentrations of about 10%. The sugar concentration in foods must be higher than 50%. Despite this, condensed milk is conferred by the moderately high concentrations of lactose.

g. Filtration is the process of separation of microbes from liquid foodstuffs by using the filter sterilization. Liquid foodstuffs: wine, beer, cider, fruits juices, maple syrup and soft drink. h. Irradiation is the process of preservation food by using light. It does not involve food heating. Food irradiation converts water to hydrogen peroxide and by generating free radicals that react with cellular components.

It may produce unacceptable changes (causing odours and unpleasant tastes). It has been employed to prolong the shelf life of soft fruits such as strawberries. Low-dose irradiation eliminate of salmonellas from poultry and to suppress the spoilage flora found on meats, poultry and fish. i. Vacuum packaging Is another that can help preserve the food. --absence of O2 --increase of CO2

2. Chemical method --sage, rosemary, garlic, onion --vinegar (pH too low for the growth) --smoking (70 C for 30min) --formaldehyde --phenolic --cresols

2. Chemical method --sodium benzoate --sulphur dioxide --sodium metabisulphite --salt of sorbic and propionic acid --nitrate, nitrite

conclusion Through the article, we know why and how the foods are spoiled, then we can preserve them by various methods such as pasteurization, filtration and chemical substances.

Thanks for your attention