Taking the good with the bad

There are over 400 types of bacteria in the human digestive system and many of these are good bacteria which help the organ system do its job. Good bacteria promote health and break down plant starches and other foods that are otherwise tough   for our body to digest; they allow the body to convert more food into energy,writes Varshaa B S

Ever wondered how the human body works in such a clockwork manner? The answer lies in the many micro-organisms responsible for the systematic functioning of our body and for ensuring that it is in good condition, in spite of illness and ageing.

We are talking about bacteria that are supportive of our digestive system. There are over 400 types of bacteria in the human digestive system and many of these are good bacteria which help the organ system do its job. Good bacteria promote health and break down plant starches and other foods that are otherwise tough for our body to digest; they allow the body to convert more food into energy. 

Bacteria help in breaking down of drugs and carcinogens which can cause cancer and also help the walls of the digestive tract to renew themselves regularly so that the human body can be rid of damaged cells that could lead to cancer.

Good & friendly 

Although good bacteria find their way into the human digestive system naturally, they are wiped out of the body with the bad ones due to antibiotics and stomach viruses. The body does build up its supply of good bacteria naturally, but it is also possible through probiotics.

Probiotics, often called ‘friendly’ or ‘good bacteria’ are live lactic acid producing micro-organisms, most commonly lactobacillus, similar to those found in the human digestive tract. They are available as nutritional supplements and also in yogurt, infant’s formula and some other foods.

The majority of probiotic microbes are members of the lactobacillus or bifidobacterium genera. Many species, sub-species and strains exist within these two categories. They include:

*Lactobacillus acidophilus: It is one of the most common and versatile probiotics used in yogurt cultures. 

*Lactobacillus rhamnosus: Its medicinal effects are similar to L.acidaphilus. It has proven to have beneficial effects on intestinal immunity.

*Bifidobacterium animalis: This has the  ability to improve digestion regularly.

*Escherichia coli: These are rarely good species of bacteria but some nonpathogenic strains have therapeutic value. Friendly strains of e.coli can prevent and treat ulcerative colitis.

*Lactococcus lactis: It has limited medicinal value but its strains are present in all forms of cheese and buttermilk.

*Lactobacillus reuteri: It is also called the universal probiotic found in the colons of most animals where it fights out pathogenic bacteria. The immunosupportive and anti-gas effects associated with breastfeeding in humans is due to the presence of this bacteria in human breast milk.

*Lactobacillus delbrueckii subspecies bulgaricus (LAB): They have anti-mutagenic effects. Animal studies have shown that some LAB have evidence for acting against colon cancer in rodents and are also able to lower serum cholesterol. 

How they survive

Some factors, both intrinsic and extrinsic, may influence the survival of probiotics in food and have to be considered in all stages of probiotic food manufacturing such as:

Physiological state: The physiological state of bacteria when prepared and remaining in a product itself are important factors for survival of the probiotics. Dryness in a food product keeps it in a relatively quiescent state during storage.

Temperature: Temperature affects the shelf life of the bacteria — low temperature providing conditions for possible long-term survival. 

The temperature at which probiotic organisms grow is an important factor in food applications where fermentation is required. During processing, temperatures over 45-500 C (113–1310F ) will be detrimental to probiotic survival.

 Producing and maintaining low water activities in foods is the key to maintain probiotic viability during non-refrigerated storage because there is a remarkable interaction between temperature and water activity.

pH levels

Some bacteria like lactobacilli and bifidobacteria can tolerate lower pH levels because they produce organic acid and products from carbohydrate metabolism. In fermented milks and yogurts with pH values between 3.7 and 4.3, lactobacilli are able to grow and survive, while bifidobacteria tend to be less acid tolerant.

B.animales subspecies. lactis is commonly used in acidic foods because it is more acid tolerant than human intestinal species. Survival of lactobacilli in low pHs can be enhanced in the presence of metabolisable sugars and this can improve survival during gastric transit.

Water activity: The higher the moisture levels and water activity, the lower the survival of probiotic bacteria. 

Oxygen: Both bifidobacteria and lactobacilli are anaerobes and oxygen can be detrimental. However, the degree of oxygen sensitivity varies considerably between different species and strains. Although probiotic bifidobacteria do not grow well in the presence of oxygen, many have enzymatic mechanisms to limit oxygen toxicity. For oxygen sensitive strains, some strategies like usage of antioxidant ingredients, or use of oxygen barrier or modified — atmosphere packaging can be used to prevent oxygen toxicity in food products.

Toxicity of ingredients: Interactions between probiotics and other ingredients could happen and those can be protective, neutral or detrimental to probiotic stability. The inclusion of antimicrobial preservatives, elevated levels of ingredients such as salt, organic acids and nitrates can inhibit probiotic survival during storage.

Freeze-thawing 

Freezing probiotics is detrimental for survival of bacteria as their cell membranes are damaged and also make the cells more vulnerable to environmental stresses. To prevent or at least mitigate cell injury, protectants are usually added to cultures to be frozen or dried. 

Slow-cooling rates or pre-freezing stress are alternative methods of freezing and improve cell survival. But repeated freeze-thawing cycles are highly detrimental to cell-survival and should be avoided.