By “shopping cart commodities” are meant animal products like meat, poultry, eggs and fish, on the one hand, and plant products like vegetables, fruits and flowers, on the other. With a nutriological point of view, vegetables and fruits are similar in their effects on human health, supplying minerals, vitamins, spicy materials and fiber. Though they also provide some carbohydrates and protein, vegetables and fruits are used mainly to supply the nutrients deficient in grains and animal products. 

A. Dietary Fibers

    Dietary fiber is now called by some people “the seventh nutrient”. 

“Dietary fiber” is a general term referring to all the materials in plant foods which cannot be digested by the digestive enzymes in the human body. By their chemical structure, dietary fibers can be divided into two groups: non-starchy polysaccharides and lignin. Polysaccharides include cellulose and non-cellulose polysaccharides i.e. hemi-cellulose, pectin, gum, and the like. By their solubility, they are divided into insoluble (non-hydrophilous) fibers and soluble (hydrophilous) fibers; the former include cellulose, lignin and most hemi-celluloses while the latter pectin, gum, viscose, algin and some hemi-cellulose. Insoluble dietary fibers are excreted from the body in their original forms together with the feces. Soluble fibers are partly degraded by the bacteria in the colon intestines, producing hydrogen, carbon dioxide, methane, water and short-bond fatty acids. Through ion exchange, insoluble fibers can combine with cholic acid in the intestines. The amount of cholesterol used to synthesize bile acid increases, resulting in a drop of cholesterol level in the blood. The short-bond fatty acids resulting from the glycolysis of soluble fibers decrease the acidity in the intestines, thus inhibiting the formation of carcinogens and facilitating their discharging from the body. Soluble fibers function to increase the volume and softness of the feces, thus facilitating laxation and preventing constipation. What has been mentioned above shows that soluble fibers are far superior to insoluble fibers in their healthy-promoting functions, and they are more acceptable to consumers owing to their good palatability?

    The fibers contained in ordinary vegetables are insoluble. In contrast, glucomannan -- the major active component of konjac, is a soluble hemi-cellulose. Its outstanding health-promoting function lies in its regulation and correction of nutrient unbalance in dietary fibers. Its primary functions are:

1. Prevention and treatment of constipation

    Sufferers from constipation are increasing in number as the food quality of the average people improves and life expectancy lengthens. To increase the content of dietary fibers is the main approach for constipation prevention. Konjac falls into the category of high dietary fiber food.

2. Regulation of lipid metabolism

    At the present time, coronary heart disease has become one of the main causes for human deaths. Zhang Maoyu et.al. Showed in their study (1989) that cholesterol level in the serum was closely related to the incidence of athero-sclerosis and coronary heart disease. Soluble dietary fibers combine with the cholic acid in the intestines, increase its excretion, enhance its synthesis in the body and, as a result, lower cholesterol level in the blood. They also help decrease the formation of gall stones when bile is released from the bile tract and alleviate the possible carcigenous effects of the metabolites of the bile acid. It is documented that insoluble crude fibers have no blood-fat lowering effect, while soluble fibers are effective to lower blood fat level. It is reported many countries that konjac can significantly lower the level of cholesterol and triglyceride in the blood, and blood fat level will not continue lowering once the normal level is reached. So konjac helps to regulate lipid metabolism and prevent hyperlipemia.

3. Improve sugar metabolism

    Diet control is an important measure in treating diabetes. Dietary fibers are considered as a good supplementary medicine for diabetics since they cannot be digested and absorbed, contain no calories, give a feeling of stomach fullness and reduce or retard glucose intake. It is reported that soluble fibers alone, instead of insoluble fibers, have a conspicuous effect of improving sugar metabolism. Huang Chengjue et.al. Reported that administering semi-purified konjac powder, i.e.crude konjac glucomannan (crude KGM), or konjac diet to diabetics lowered the blood sugar level in their body.

4. Slimming effect

    Walsh, an American scientist, verified the slimming effect of konjac by “double blind” method. Chinese researchers provided further support to the claim that dietary fibers filled the space in the stomach with a resulting feeling of fullness and decreased the intake of nutrients by the human body. Therefore, supplementation of appropriate amount of konjac in the diet can help prevent diabetes and gradually lose weight.

5. Other desirable functions of konjac

    It is well-documented that many kinds of non-starchy polysaccharides can regulate the immunity function of the body. They can enhance non-specific immunity, cell immunity and/or body fluid immunity. Peng Shusheng et.al. demonstrated in their experiment with mice that crude KGM improved the specific and non-specific immunity functions of normal and abnormal (with suppressed immunity) mice, thus confirming its immunity-regulating function.

Epidemiological investigation and some experiments showed that dietary fibers help, to some extent, prevent colon cancer and breast cancer. The mechanism for such a function may be that soluble cellulose absorbed great amount of water, thus diluting the concentration of carcinogens and pre-carcinogens in the intestines and facilitating their removal from the body. Zhang Maoyu et. al. reported that soluble cellulose influenced the bacterial composition in the intestines with an increase in the number of anaerobic bacteria. Bacteria in the genus of Bifid bacterium, which are anaerobic, are known to help resist cancers by accelerating the excretion from the body of the suspicious carcinogenous metabolites of bile acid.

    In short, as far as the healthy and healing functions of dietary fibers in the above-stated five aspects are concerned, glucomannan, the primary component of konjac, is far superior to and other insoluble fibers contained in ordinary vegetables.

B. Glucomannan

1. Chemical composition of konjac

    The genus Amorphophallus of Araceae family has more than 170 species, which may be divided into three types according to their chemical composition: KGM-type, starchy type and intermediate type. The primary component in KGM type is konjac glucomannan (KGM). Their representatives are white konjac (A. albus) and colored konjac (A. konjac), which are cultivated for their KGM. The starchy type has starch as its primary chemical component and, therefore, is used as animal fodder or processed for its starch. The third type is intermediate between the two. The dominate cultivated varieties, white and colored konjac, contain 49-60% KGM, 10-30% starch, 2-5% fiber, 5-14% crude protein (including amino acids),3-5% soluble sugars (including monosaccharide and oligosaccharide) and 3.4-5.3% ash (minerals) in their stem base. They contain 8 essential amino acids (2.616%) and 10 non-essential amino acids (7.881%) and are low in vitamins and fat. Their corm and leaves contain a small amount of alkaloid, saponin and stimulating substances.

    Konjac corms are oven-dried and broken into chips, which are then crashed to obtain konjac meal. When konjac meal is ground and starch and other substances are removed in the process, semi-purified konjac powder (crude KGM) and flying powder (starch and impurities) will be separated. Though flying powder has higher value from a nutritionist point of view, konjac powder is far more valuable economically and has a wider prospect for development and exploitation. When crude KGM is further purified and microsized, konjac gum will result.

2. The structure of KGM

    KGM, a high molecular polysaccharide, is formed when the residues of glucose and mannose are bound together by β-1, 4 glycoside. On C-3 of some glucose residues are side chains composed of β-1, 4 glucose residues. On the main chain, 1 side chain occurs per 3,280 glucose residues, and on each side chain are several or dozens of glucose residues. On the average, 1 acetyl is bound to the side chain per about 19 glucose residues. The molecular weight of KGM varied from 200,000 to 2,000,000 with konjac species or variety, processing method and storage time of the raw material. The molecular weight of KGM of A. albus is greater than that of A. konjac.

    The molecular weight of wet processing is greater than that of dry processing. Molecular weight decreases with heating temperature and duration in processing and with storage duration.

3. The physico-chemical properties of KGM

    KGM is water soluble and can be as a thickening, stabilizing, suspending, film-forming and viscosifying agent.

    a) Water solubility: KGM is readily dissolved in water and it can absorb 100-fold as much as water in volume. Its water solution is a pseudo-plastic liquid, characterized by shear thinning.

    b) Thickening: Owing to its great molecular weight, high hydration capacity and freedom of charges, KGM is a good thickening agent. The viscosity of 1% crude KGM is as high as several thousand mPa.s or even 200,000 mPa.s, higher than any other natural thickening agents. KGM also shows a synergistic effect with other thickening agents like xanthan gum. For example, the addition of 0.02-0.03% crude KGM to 1% xanthan gum will raise its viscosity by 2-3 times under heating.

    c) Stabilizing: Unlike xanthan gum, guar gum or locust bean gum, konjac gum is of the non-ionic type and is therefore little influenced by the salt in the system. At ambient temperature, konjac gum remains stable without precipitation even if the pH drops to a level below 3.3. When konjac gum is used instead of locust bean gum as the stabilizing agent and added to ice cream, cheese and other dairy products, it will stabilize their quality by preventing the development of ice crystals.

    d) Jelling: In food industry, many kinds of products rely on the jelling property of hydrophilic colloids to form their special shape or structure and to guarantee their timely thaw at a certain temperature. Carrageenam gum, pectin, gelatin and sodium alginate fall into this category. As a jelling agent, KGM is quite unique for its ability to form thermo-reversible and thermo- irreversible gels under different conditions. Therefore, this property of KGM is exploited to produce many special varieties of foods.

    Xanthan gum does not gelatinize when used alone but can form gel at any pH when used in combination with konjac gum. At a pH of 5, the two gums show a greatest synergistic effect and when xanthan gum is used with konjac gum at a ratio of 3:2, the greatest gelatification will be achieved. This gelatification of the compound gum behaves as heat reversible: it appears in the solid state under indoor temperature if only it is no higher than 40oC; it will be in a semi-solid or liquid state at 50oC or above. When the temperature drops back to the ambient temperature, it will resume the solid state. Base on this property of the compound gum, various types of jelly, budding, jam and fat-free confectioneries can be made by adopting different concentrations of the compound gum and adjusting to different pH values.

    KGM solution does not form gel because its acetyl group prevents the long chains of glucomannan from approaching each other. However, it does form gel when heated at a pH of 9-10. This gel behaves stable to heat and it will remain stable under repeated heating at 100oC or even at 200oC. That is why this gel is called non-reversible gel, whose mechanism is that the acetyl deviates from glucomannan in a naked state when heated under an alkali condition and partial structural crystallization occurs due to the formation of hydrogen bonds between molecules. And KGM becomes stable due to the formation of a net-like structure with the crystals as nodes.

    Making use of the heat non-reversible property of the konjac gum, it may be used to make a great variety of foods, such as konjac cake, konjac chips, konjac slices, konjac noodles, and animal food-imitating foods for vegetarians.

 C. Konjac foods

konjac is a pollution free food

    Konjac is generally grown in mountainous regions at relatively high altitudes. Such regions are free from the air and water pollution in the urban areas. In its cultivation, little or no chemicals with residual toxicity are applied (the diseases of Erwinia carotovara var. carotovara and Sclerotium rolfsii Sacc. Are controlled by streptomycin and lime, respectively), and therefore, the raw material is free from pollution. The equipment for food processing is manufactured with material inl line with the requirements of food production. For its preservation, pure calcium hydroxide is used. Therefore, konjac is entitled to be calling a “green food”.