Types of Oriental Foods | Microbiology

In this article we will discuss about the mycoprotein and food—feed source types of oriental foods that are used in many countries including India.

1. Mycoproteins:

Traditionally, oriental foods are used in many countries including India. Products such as tempeh and koji contain a significant amount of mold biomass (mycelium) which is a source of food.

Myco-proteins, marketed in some foreign countries under the name Quom, is essentially the mycelium of Fusarium gramineramm grown in continuous culture in a medium containing glucose, ammonium salts and a few growth factors.

It is essential to reduce the level of RNA which is about 10% on mycehal dry weight to below the levels likely to lead to kidney stone formation or gout. This can be achieved by mild heating prior to filtration which activates the RNases and leads to RNA reduction. Such products contains 44% of protein and is high in ‘fiber’ contents.

(i) Tempeh:

This is the fermented food of Indonesians. The most popular type is produced from soybeans and also called as tempeh kedele. Whole clean soybeans are soaked overnight in water to hydrate the beans. A bacterial fermentation occurs decreasing pH to 4.5-5.3.

The beans are de-hulled and the moist cotyledons cooked resulting pasteurization of the substrate. It destroys the trypsin inhibitor and lectins contained in the beans. After cooking, the beans are drained and spread on to bamboo trays for cooling.

The fermentation is carried out by mixed cul­ture of molds, yeasts and bacteria but most important component appears to be Rhizopus oligosporus. After 48h incubation at 33-35°C, the mycelium develops, pH rises to around 7, fungal protease increase the free acid content of the product and lipases hydrolyse over to neutral fat present to free fatty acids.

Fresh tempeh has a nutty odour and flavour which can be consumed after frying in oil. Except thiamine, other vitamins increase to varying degree during fermentations. Tempeh is the impor­tant source of vit.B 12 for people subsisting on a largely vegetarian diets.

Tempeh has been stopped from 1988 due to food poisoning by Pseudomonas growing in the product and elaborating the toxious acid production.

(ii) Soy Sauce:

This is a representative of product which have mold activity in two stage fermentation process:

(a) Koji Stage:

The production of the soy sauce involved two stage fermentation process. The molder starter used is often called koji. In case aerobic conditions allow molds to grow on the substrate producing a range of hydrolytic enzymes. The soybeans are mixed with roasted wheat in equal proportions and inoculated with seed koji. i.e. a mixture of substrate and strains of Aspergillus oryzae. The moulds are grown about 5 cm deep for 2-3 days at 25-30°C (Fig. 21.4).

(b) Moromi Stage:

Moromi stage is a mash process in which conditions are made so as not to allow molds to grow. In soy sauce production this is obtained by mixing koji with an equal volume of brine to give a final salt concentration of 17-20%. The yeasts and lactobacilli dominate the microflora produced a number of flavoured compounds and convert half of the soluble sugars to lactic acid (2-3%) and ethanol (1%).

The halophiles lactic acid bacterium Tetragenococcus halophilus (formerly Pediococcus halophillus) and the yeasts Zygosaccharomyces rouxi and Torulophilus, etc. have been identified as being important organisms.

This stage lasts up to a year or more at the end of which the mash is filtered to remove the solid residues which may then be mixed with brine to undergo a second fermentation and produce a lower grade product. After pasteurization, filtration and maturation the product is bottled.

(iii) Miso:

Molds are involved in the prepara­tion of most of the oriental foods. Miso is prepared by the starter termed koji (by Japanese) and chou (Chinese), molds serve the source of enzymes. In this case Aspergillus oryzae is used to ferment steamed polished rice in shallow trays at 35°C.

The koji is mixed with a mash of crushed and steamed soybeans to which salt is added. The fermentation is now allowed for about 6-7 days at 28°C and 60 days at 35°C. Finally, it is ground to form a paste which is used with other foods.

(iv) Idli:

It is a fermented food of southern India and is delicacy of the dinning table of Northern Indians. It is a product made from rice and black gram (Vigna mungo) in equal parts. After soaking overnight in water, both the ingredients are washed, mixed and ground, fermented overnight at room temperature. When the batter has risen enough, it is cooked by steaming.

Leuconostoc mesenteroides grows first in batter, leaving it, and is followed by Streptococcus faecalis:

(v) Natto:

It is a soybean made product. The soybeans are wrapped in rice straw and fermented for 1-2 days. The package becomes slimy on the outsides. The microbe involved Bacillus natto, grows in natto, release trypsin like enzymes responsible for ripening process.

(vi) Minchin:

In this case starch free but gluten rich wheat is used. The moist raw glutens placed in a closed jar and allowed to ferment for 2 to 3 weeks, after which it is salted. A typical specimen was found to contain several species of molds, some of bacteria and a few of yeast, the final product is boiled, baked or fried.

(vii) Poi:

The bulbs and the corns of the taro plant are steamed for 2-3 hours, cooled, trimmed, scrapped and then finally ground. It is mixed with water as per desire and then can be consumed. On the other hand, if fermentation is carried out at room temperature for at-least a day during the first 6 hours of fermentation, the poi swells or puffs slightly with a change in the colour.

After this, certain microbes in particular Pseudomonas spp., chromogenic bacteria, coliform group of bacteria become prominent. Lactobacillus pasteurians, and L. delhruckii, L. brevis, Streptococcus lectis sub sp. lactis and S. kefir consist of predominant flora. The fruity odour and pleasing taste impart in poi by the cultures of Geotrichum candium. The abnormal fermentations are likely to be of the butyric acid type.

2. Food—Feed Source:

Yeast such as Saccharomyces cerevisiae (sak-q-ro- raises se-ri-visei) or Candida utilis can be grown in large quantities, but they lead to adverse gastrointestinal reaction in humans. Also their high nucleic acid content exceeds the human body’s capacity to metabolize them and may precipitate ailments such as gout.

Yeasts are, therefore, most likely to be used as an animal food supplement. Microbes, which can usually double their weight in few hours and often in less than an hour, may solve this problem. When used as a food source, microbes are referred to as single cell proteins (SCP).

Types:

(i) Baker’s Yeast:

Those strains which give good yield of cells, efficient sugar fer­mentation, easy mixing in water, etc. are used in the mash or medium chosen for their cultivation, should be stable, should remain viable in the cake or dried form for a reason­ably long period, and should produce CO₂ rapidly in the bread dough when used for leavening.

The starter culture should be built from the original mother culture through several intermediate cultures and the commercial production of baker’s yeast is on cane or beet molasses, or mixture of both mineral salts mash that contains molasses, nitrogen in the form of ammonium salts, urea, malt sprouts, etc., inorganic salts as phosphates and other mineral salts, and accessory growth substance, grain or yeast, or small quantities of vitamin precursors or vitamins such as biotin, pentothenic acid and inositol. The pH is adjusted to about 4.3 to 4.5, and the incubation temperature is around 30°C.

During the growth of the yeast the medium is altered at a rapid rate, and molasses is added gradually to maintain the sugar level at about 0.5-1.5%. In the beginning, the culture is aerated but after 8-12 hours its rate is decreased.

Addition of sugar and ammonia is checked. After 4-5 budding cycles, the yeast is centrifuged out in the form of a cream which is put through a filter press to remove excess liquid. The mass of yeast is made into cakes of different sizes after incorporation of small amounts of vegetable oils (Fig.21.5).

Active dry yeast now is made by drying the yeast cells to less than 8% moisture. Cells so dried are grown especially for the purpose and are dried carefully at low temperature^^ that most of the cells will survive and will retain for some month their ability to actively leaven dough.

Baker’s yeast can be prepared from grain mashes, waste sulfite liquor from paper mills, wood hydrolysate, and other materials. The commercial production of baker’s yeast involves the development of an inoculum through a large numbers of aerobic stages.

Although, the production stages of the process may not be operated under strictly asep­tic conditions, a pure culture is used for the initial inoculum, thereby keeping contamination to a minimum in the early stages of growth. Reed and Nagodawithana (1991) discussed the devel­opment of inoculum for the production of baker’s yeast and noted a process involving 8 stages the first 3 being aseptic while the remaining stages were carried out in open vessels.

(ii) Mushroom Nutriceuticals:

According to a UNESCO sponsored symposium held in Manila 1993, nutraceuticals are a new class of compounds extractable from either the mycelium or fruiting body of mushrooms. The term neutriceutical comprises of both the nutritional and pharmaceutical (i.e. medicinal) features.

These are consumed in the form of capsules or tablets as a dietary supplements and have potential therapeutic applications. A regular intake enhances the immune response of the human body’ thereby increases the resistance to disease. In some cases, it causes regression of a disease state.

Application:

Preparations of Lentinus edodes and Schizophyllum commune are the examples. Lantinan (a purified polysaccharides used in the treatment of certain cancers and infectious diseases) and Schizophyllum (extract used to treat cervical cancer) are pharmaceutical products.

Ganoderma lucidum, an important medicinal fungus, has multi-beneficial effects on viscera, the audio and visual and olfactory sense, to improve intelligence, enhance the memory, and to related the aging process.

Several hepato-protective triterpenoids and carcinostatic polysaccharides have been isolated from the basidiocarps and mycelia of G. lucidum and G. tsugul. Auricularia spp. have traditionally been used to treat haemorrhoids and various stomach ailments, while Volvariella volvacea for lowering the blood pressure, and Tremella fusiformis for sufferers of gastric ulcers have been reported.