Chinese scientists have made a splash in the international circuit recently by claiming the development of a technology to make low carbohydrate juice products from vegetables like carrot using lactic acid fermentation and further claiming that these products are good for diabetic people. What is not clear in this claim is whether they have found a new strain of microorganism that will 'eat up' complex carbohydrates like starch present in many vegetables. Use of Lactic Acid Bacteria (LAB) in many traditional vegetable products is ancient dating back to centuries and many traditional foods in Asian and African continents are based on this fermentation. Professor Steinkraus, an internationally acclaimed and highly knowledgeable microbiologist, has brought out an epic book on the fermented foods which is virtually an encyclopedia on the subject. It is difficult to understand what is new in the present findings reported by Chinese scientists. Lack of any substantial data on their study makes it difficult to come to any meaningful conclusion.
To begin with most vegetables are low in carbohydrates including sugars and their consumption is recommended because of this reason. Besides they are rich in dietary fiber, several vitamins and essential minerals. The carbohydrate content in most of the vegetables vary from 2.5% in bitter gourd to 9.7% in carrot but is high in some like Peas (14.4%) potato (22.1%), Yam (18.4%), Breadfruit (15.8%) and Plantain (14%). There are many vegetables grown in India with low carbohydrate content like bottle gourd (2.5%), brinjal (4%), squash (3.4%), okra (6.4%), snake gourd (3.3%), pumpkin (4.6%), ridge gourd (3.4%), spinach (4.3%), radish (3.4%), and tomato (4.7%). More over the glycemic index (GI) of of most of the vegetables is very low because whatever little carbohydrates present in them, are encased in so much cellulosic material that they cause practically no rise in blood sugar even if consumed in large quantities. Only some like Potato ( GI 80+), Peas (GI 48), Corn (GI 53) and Carrot (GI 47) are considered having some what higher GI values. Vegetables are rich sources of dietary fiber, both soluble as well as insoluble and many of them contain 2-6% fiber, considered vital for good health. If this is so where is the need to reduce the carbohydrate involving costly technological intervention which will also remove the beneficial dietary fiber and other nutrients in the process? Nonetheless LAB fermentation process does not involve heating of the raw material and there fore the products may contain some health protecting phytonutrients like isothiocyanates in significant quantities generated by live enzymes like myrosinase.
If the purpose is to make drinkable juice products, use of pectinase can serve the same purpose faster. Subjecting vegetable pulps to LAB fermentation is time consuming and cumbersome and the products will have a distinct acidic taste which has to be adjusted to suit the palates of the consumers that calls for significant dilution. Again addition of salt or sugar may be necessary to make the product palatable especially to young age consumers. A 3/4 cup juice is supposed to be equivalent to one serving of vegetables and if 5 servings are to be made, almost 4 cups of juice will have to be consumed requiring at least 4 g of salt to make them palatable! It is true that health freaks are already consuming such juices from many vegetables and herbs but their number and quantities consumed are rather limited raising a question regarding the commercial viability of these LAB fermented vegetable juices.
LAB group consists of homofermentors and heterofermentors, converting sugar to lactic acid and CO2 or a mixture of lactic acid, acetic acid, ethyl alcohol and CO2 respectively. These include Lactobacillus acidophilus, L.bulgaricus, L.plantarum, L.caret, L.pentoaceticus, L.brevis and L.thermophilus. Streptococcus and Leuconostoc species also produce lactic acid but much less than that produced by Lactobacillus species. They are all microaerophilic organisms requiring no oxygen for their growth and metabolism. Traditional sauerkraut fermentation of cabbage brought about by Leuconostoc mesenteroides is a classical example of lactic acid preserved vegetable, consumed widely by Europeans. There are typical traditional fermented products in many countries, almost all of them preserved by lactic acid fermentation in presence of salt. Kimchi of Korea, Gundruk of Nepal, Kocho of Ethiopia, Pak-gard-dong, Hum-dong, Hua-chai po and Naw-mai-dong of Thailand, Hum choy and Tai-tan-tsoi of China, Tempoyak of Malaysia, dozens of pickles from mango, lime, gooseberry etc in India, are all LAB mediated preserved foods that have stood the test of time for centuries.
The critical substrate for LAB is sugar and only in case of vegetables that contain small concentration of sugar can initiate fermentation. The role of the salt is primarily to bring out the juice and subsequent liberation of sugar for further action by the microbes. During LAB action glucose is broken down mainly to lactic acid and lactate which enters the blood when pickles are consumed is converted to pyruvate in the liver for deriving energy through the Kreb's Cycle. Excess accumulation of lactate in the blood can end up as glucose through the pyruvate route. Though lactic acid fermentation does bring down carbohydrate load, it does not guarantee against rise in blood sugar in the blood under certain conditions. While LAB fermented vegetable juice products can be a separate category of newly developed beverages which should stand scrutiny of the consumer for its acceptability, claiming it to be a panacea for diabetic people is some what far-fetched!