Polysaccharides. Группа авторов
Mitsumame, a fruit dish of Portugal and Japan, requires agar with elevated melting point. Sometimes acidification is required in food processing and needs to be done only at lower temperature and when agar is completely dissolved, since it can hydrolyze the agar in food. Likewise, the aromas should be added only when product is complete to avoid evaporation loss. However, agar has lower degree of hydrolysis even at high temperature. It is noticeable that during meat preservation, sterilization is required and is done at 121 °C, still agar doesn’t get hydrolyzed. An average of 0.5 to 1.5% agar is added to foods, since human digestive system cannot absorb much of it. It is reported that less than 10% of ingested agar is digested.
This encourages the use of agar in dieting industry. Moreover it doesn’t get digested and has no impact upon human health and can be used as dietary food stuff for diabetic patients. Unlike pectin, which requires sugars to gel, agar can be easily used as food stuff in medical industry. Like in diabetic patients, artificial sweeteners, as sugar substitute, can be added to agar to create a very least calorie food. Region-wise global agar applications in food industries are given in Table 5.3.
5.9.2 Application of Agar in Harvesting Insects and Worms
In insect culture, agar is utilized as food agent to feed the insects. Agar is utilized for the reproduction of larvae as well as for different tiny animal species. Majorly in silk producing insects, agar is used as a food agent. Tiny silk worms only feed on the tender mulberry leaves. These leaves can only be found in the early budding stages of the plants. Here agar, mixed with all essential nutrients, is used to feed the tiny silkworms. Other gelling products are useless here, as they have some taste in them therefore silkworms reject them easily.
Furthermore, agar is also used as food agent to feed Drosophila melanogaster larvae. In genetic research, different harmful insects are prepared in labs and then they are sexually sterilized using gamma radiation and then kept for hibernation until use. Later these insects are set free during the mating period in fields or in the area where, their population is higher. These sterile individuals mate with the fertile insects, making them ineffective, because these organisms mate only once in their whole life. Their copulation gets exhausted and they are now no longer able to mate with the other healthy insects, thus making other insects useless too.
5.9.3 Vegetable Tissue Culture Formulations
Agar provides a good solid base as a medium in tissue culture techniques. Agar was primarily used as a medium in the development of orchid clones. Since agar media is autoclavable and can be sterilized easily, it can be easily used in plant tissue culture to produce identical virus-free plants also known as monoclonal culture. Generally vegetative parts of plants are grown in agar medium, enriched with adequate chemical nutrition like vegetative hormones such as auxines and cytokines. As the adequate plant growth has been developed, under sterile conditions, these plants are transferred into their respective wild fields/areas.
Table 5.4 Different types of agar medium with respective uses and description.
| Type of agar | Their brief description and uses |
| XLD agar | Xylose lysine deoycolate is an agar with two markers. Suppresses the growth of Gram-positive bacteria and promotes growth of Gram-negative bacteria. Uses in fecal culture. Lactose fermenting bacterial colonies appear yellow in it. |
| Blood agar | An almost complete nutrient-rich media, prepared from animal blood. Supports most bacterial growth. |
| Tryptic soy agar | Provides basic medium to culture several types of microbes. Primarily used as initial growth medium to monitor colony morphology. |
| Chocolate agar | Made from sheep blood, that gives X and V factors, which are important for Haemophilus growth. A nutritional medium for fastidious microbes like Neisseria and Haemophilus species. Conversely, it doesn’t provide haemolysis data of microbes, so species differentiation among the members of Haemophilus are carried out separately. |
| Thayer-Martin agar | Similar to chocolate agar, designed to isolate Neisseria gonorrhoeae aka gonococcus. A Gram-negative bacterium which causes gonorrhoea. |
| LB (Luria Bertani) agar | A counterpart of nutrient agar. Broadly used for isolation of unknown microbes. Doesn’t allow over lapping of microbial colonies. |
| Sabouraud agar | Primarily used in fungal culture at low pH. Lower pH also eliminates most of the bacteria. Encloses gentamicin, an aminoglycoside antibiotic. Gentamicin helps in treating bacterial infections, especially Gram-negative infection. |
| MacConkey agar | An agar, prepared in such a way that it only supports Gram-negative bacterial growth. Already encloses pH indicators. For example: Escherichia coli colonies reflect red colour as a pH indicator. MacConkey agar comes in two types: with sugar lactose and without sugar lactose. As E.coli ferments sugars into acids and gives red colour due the presence of pH indicator, one can actually add desired sugar into ‘sugar free’ MacConkey agar and predict desired microbial colony. |
| Nutrient agar | Supports the largest number of microbial growth of bacteria and fungi. Still very uncertain for many bacteria, it is overly nutritional for some bacteria and deficient for some bacteria, at the same time. Beef extracts and yeast are the nutritional components of this agar. |
| Miller’s LB agar | Miller’s LB agar is a counterpart of Luria Bertani agar. It has the same ingredients as LB agar, but the quantity is different. |
| Non-nutrient agar | Non-nutrient agar is used for the culture of microbes other then bacteria. |