FACTORS AFFECTING MICROBIAL GROWTH IN MILK Factors Affecting

FACTORS AFFECTING MICROBIAL GROWTH IN MILK

Factors Affecting Microbial Growth 1. Intrinsic Parameters (inside the milk) üFactors inherent to the food (chemical and physical) ücharacteristics of food üp. H üMoisture üOxidation-Reduction Potential Inside Food üNutrient Content üNatural Antimicrobial Constituents üBiological Structures & Natural Microflora

2. Extrinsic Parameters (environment around the milk) üStorage conditions of the food i. e. properties of the environment in which the food is stored üTemperature üRelative Humidity üPresence of Gases or Oxygen üAntimicrobials or Added Microorganisms

p. H üMicroorganisms sensitive to changes in acidity because H+ and OH- interfere with H bonding in proteins and nucleic acids. üMicrobes have no mechanism for adjusting their internal p. H. üTherefore, p. H of food significantly affects the microbial growth on it.

MOISTURE CONTENT • The effect of moisture is in terms of water activity: the amount of free water in a food medium. • The amount of free water is important for growth of microorganisms. • If there is lack of free water microorganisms will not grow. • Salting and drying reduces the water activity of a food product.

NUTRIENT CONTENT §Microorganisms require energy source such as carbohydrates, amino acids, proteins, organic acids and alcohol. §Nitrogen source such as amino acids, peptides, nucleotides, urea, proteins and ammonia. §Carbon source §Minerals such as phosphorus, iron, manganese, magnesium, calcium and potassium. §Vitamins and other growth factors §Milk being a rich source of all the above gets easily spoiled by the micro-organisms.

PRESENCE OF ANTIMICROBIALS §Natural constituents of foods which affect microbial growth are: Lactoferrin e. g. Milk §Lactoperoxidase e. g. Cow’s milk §Conglutinin e. g. Cow’s milk §These antimicrobials help preserve milk for longer period of time.

MICROFLORA IN MILK §In addition to being a nutritious food for humans, milk provides a favorable environment for the growth of microorganisms. §Yeasts, moulds and a broad spectrum of bacteria can grow in milk, particularly at temperatures above 16°C. §Microbes can enter milk via the cow, air, feedstuffs, milk handling equipment and the milker. §Once microorganisms get into the milk their numbers increase rapidly.

Biological structures ü Some foods have biological structures that prevent microbial entry. ü For example, meat has fascia, skin and other membranes that prevent microbial entry. ü Eggs have shell and inner membranes that prevent yolk and egg white from infection.

Extrinsic factors v External to the food that affect microbial growth. They include: 1. Temperature of storage, 2. Presence and concentration of gases in the environment 3. Relative humidity environment. of food storage

Temperature ü The growth of microorganisms is affected by the environmental temperatures. ü Various microorganisms are able to grow at certain temperatures and not others. ü Bacteria can therefore be divided into the following groups depending upon their optimum tmperature of growth. ü The effect of temperature on microbial growth also depends upon other environmental conditions such as: Growth factors in the nutrient medium, p. H of the food, and Water activity.

Concentration of gases in the environment v This relates to the presence and concentration of gases in the food environment. v Various microorganisms require for growth, either high oxygen tension (aerobic), low oxygen tension (microaerobic) or absence of oxygen (anaerobic). v Some microorganisms may grow either in high oxygen tension, or in the absence of oxygen (facultative anaerobes).

Relative humidity § Relative humidiy is the amount of moisture in the atmosphere or food environment. § Foods with low water activity placed at high humidity environment take up water, increase their water activity and get spoiled easily. § For example, dry grains stored in a environment with high humidity will take up water and undergo mold spoilage.