Siok-Koon Yeo

Effect of prebiotics on viability and growth characteristics of probiotics in soymilk

BACKGROUND Soy products have attracted much attention lately as carriers for probiotics. This study was aimed at enhancing the growth of probiotics in soymilk via supplementation with prebiotics. RESULTS Lactobacillus sp. FTDC 2113, Lactobacillus acidophilus FTDC 8033, Lactobacillus acidophilus ATCC 4356, Lactobacillus casei ATCC 393, Bifidobacterium FTDC 8943 and Bifidobacterium longum FTDC 8643 were evaluated for their viability and growth characteristics in prebiotic-supplemented soymilk. In the presence of fructooligosaccharides (FOS), inulin, mannitol, maltodextrin and pectin, all strains showed viability exceeding 7 log(10) colony-forming units mL(-1) after 24 h. Their growth was significantly (P < 0.05) increased on supplementation with maltodextrin, pectin, mannitol and FOS. Additionally, supplementation with FOS, mannitol and maltodextrin increased (P < 0.05) the production of lactic acid. Supplementation with FOS and maltodextrin also increased the alpha-galactosidase activity of probiotics, leading to enhanced hydrolysis and utilisation of soy oligosaccharides. Finally, prebiotic supplementation enhanced the utilisation of simpler sugars such as fructose and glucose in soymilk. CONCLUSION Supplementation with prebiotics enhances the potential of soymilk as a carrier for probiotics.

Angiotensin I-converting enzyme inhibitory activity and bioconversion of isoflavones by probiotics in soymilk supplemented with prebiotics.

Abstract Lactobacillus sp. FTDC 2113, L. acidophilus FTDC 8033, L. acidophilus ATCC 4356, L. casei ATCC 393, Bifidobacterium FTDC 8943 and B. longum FTDC 8643 were incorporated into soymilk supplemented with fructooligosaccharides (FOS), inulin, mannitol, maltodextrin and pectin. The objective of the present study was to evaluate the effects of prebiotics on the bioactivity of probiotic-fermented soymilk. Proteolytic activity was increased in the presence of FOS, while the supplementation of inulin and pectin increased the angiotensin I-converting enzyme inhibitory activity accompanied by lower IC50 values. The β-glucosidase activity was also enhanced in the presence of pectin. This led to higher bioconversion of glucosides to aglycones by probiotics, especially genistin and malonyl genistin to genistein. Results from this study indicated that the supplementation of prebiotics enhanced the in-vitro antihypertensive effect and production of bioactive aglycones in probiotic-fermented soymilk. Therefore, this soymilk could potentially be used as a dietary therapy to reduce the risks of hypertension and hormone-dependent diseases such as breast cancer, prostate cancer and osteoporosis.

Probiotics and the BSH-related cholesterol lowering mechanism: a Jekyll and Hyde scenario

Abstract Probiotic microorganisms have been documented over the past two decades to play a role in cholesterol-lowering properties via various clinical trials. Several mechanisms have also been proposed and the ability of these microorganisms to deconjugate bile via production of bile salt hydrolase (BSH) has been widely associated with their cholesterol lowering potentials in prevention of hypercholesterolemia. Deconjugated bile salts are more hydrophobic than their conjugated counterparts, thus are less reabsorbed through the intestines resulting in higher excretion into the feces. Replacement of new bile salts from cholesterol as a precursor subsequently leads to decreased serum cholesterol levels. However, some controversies have risen attributed to the activities of deconjugated bile acids that repress the synthesis of bile acids from cholesterol. Deconjugated bile acids have higher binding affinity towards some orphan nuclear receptors namely the farsenoid X receptor (FXR), leading to a suppressed transcription of the enzyme cholesterol 7-alpha hydroxylase (7AH), which is responsible in bile acid synthesis from cholesterol. This notion was further corroborated by our current docking data, which indicated that deconjugated bile acids have higher propensities to bind with the FXR receptor as compared to conjugated bile acids. Bile acids-activated FXR also induces transcription of the IBABP gene, leading to enhanced recycling of bile acids from the intestine back to the liver, which subsequently reduces the need for new bile formation from cholesterol. Possible detrimental effects due to increased deconjugation of bile salts such as malabsorption of lipids, colon carcinogenesis, gallstones formation and altered gut microbial populations, which contribute to other varying gut diseases, were also included in this review. Our current findings and review substantiate the need to look beyond BSH deconjugation as a single factor/mechanism in strain selection for hypercholesterolemia, and/or as a sole mean to justify a cholesterol-lowering property of probiotic strains.

Effects and applications of sub-lethal ultrasound, electroporation and UV radiations in bioprocessing

Advances in bioprocess technology involving microbial cells have led to increased and improved production of beneficial new products and bioactive compounds. However, the semipermeable barrier of the cell membrane often retards the efficient productivity or reaction rate of the cells. Physical treatments such as ultrasound, electroporation and UV radiation provide an efficient approach to increase membrane permeability, leading to enhanced productivity of microbial cells. It is important to note that extensive membrane permeabilization by these physical treatments could be detrimental to cell viability leading to lower yield. An appropriate selection of sublethal dosage and intensity of these physical treatments are critical to preserve the viability of cells and at the same time maintain their bioprocess applications. Despite the promising applications of these physical treatments, safety issues related to possible genotoxicity or mutation of cells upon treatments have been raised. This genotoxic effect of physical treatments could be prevented if appropriate measures are taken, without compromising their bioprocess potentials. The current review highlights the effect of sublethal physical treatments such as ultrasound, electroporation and UV radiation on the viability of cells, their potential bioprocess applications, and the possibility of mutations.

Carriers of Probiotic Microorganisms

There is a growing market potential for probiotic foods as an alternative to enhance human health. Milk-based products including milk beverage, yogurts, cheese and ice cream are conventionally used as the most suitable delivery vehicle for probiotics. Despite being an ideal substrate for probiotics, the growth of probiotics in these products is often inhibited due to excessive acidification, antagonistic effect of starter culture and the presence of oxygen during processing. Various means are evaluated to enhance the viability of probiotics, including supplementation with growth enhancer and protection by microencapsulation. The drawbacks of milk-based carrier associated with cholesterol contents and lactose intolerance have prompted the development of alternative carriers for probiotics. Currently, new foods such as soy-based products, cereal-based products, fruits, vegetables and meat products are developed as potential carriers. These nondairy-based products contain reasonable amounts of carbohydrates, fibers, proteins and vitamins that support the growth of probiotics. In addition, some components of these products are able to protect probiotics during transit through the harsh condition of gastrointestinal tract and during storage. However, growths in nondairy products such as sausage and fruit juices are inhibited by the presence of inhibitory substances such as nisin, organic acids and curing salts. Therefore, appropriate selection of culture used in these products is crucial in maintaining the viability of cells, without affecting the sensory and organoleptic property of the final products.

Effect of electroporation on viability and bioconversion of isoflavones in mannitol-soymilk fermented by lactobacilli and bifidobacteria

BACKGROUND The aim of this study was to evaluate the effect of electroporation (2.5-7.5 kV cm⁻¹ for 3.0-4.0 ms) on the growth of lactobacilli and bifidobacteria, membrane properties and bioconversion of isoflavones in mannitol-soymilk. RESULTS The viability of lactobacilli and bifidobacteria decreased immediately after electroporation. This was attributed to lipid peroxidation, which led to alterations in the membrane phospholipid bilayer, specifically at the polar head, interface and apolar tail regions. Such alterations also resulted in decreased membrane fluidity and increased membrane permeability upon electroporation (P < 0.05). However, the effect was reversible and treated cells showed better growth than the control upon fermentation for 24 h at 37 °C (P < 0.05). Additionally, electroporation increased the bioconversion of glucosides to bioactive aglycones in mannitol-soymilk, which was attributed to increased intracellular and extracellular β-glucosidase activities of cells upon treatment (P < 0.05). CONCLUSION Application of electroporation on lactobacilli and bifidobacteria could be beneficial for the development of fermented soymilk with enhanced bioactivity. Considering the enhanced bioactive aglycones, this soymilk could be useful for the prevention of hormone-dependent disorders.

Effect of fermentation on the phytochemical contents and antioxidant properties of plant foods

Plant foods are a natural source of functional phytochemicals that can exert antioxidative effects. However, most of the phytochemicals that exist naturally in plant foods are bound and are less bioavailable than the free form. These phytochemicals and their antioxidant properties could be altered by processing, such as fermentation. The microorganisms used in fermentation are capable of modifying the bioavailability of phytochemicals in plant foods. This chapter discusses the effect of fermentation on the phytochemical contents of plant-based diets including legumes, cereals, seeds, vegetables and fruits. The chapter then discusses the changes in antioxidant properties upon fermentation and the beneficial effects on health of fermented plant-based foods.

Comparison of the Microbiological Quality and Safety between Conventional and Organic Vegetables Sold in Malaysia

Given the remarkable increase of public interest in organic food products, it is indeed critical to evaluate the microbiological risk associated with consumption of fresh organic produce. Organic farming practices including the use of animal manures may increase the risk of microbiological contamination as manure can act as a vehicle for transmission of foodborne pathogens. This study aimed to determine and compare the microbiological status between organic and conventional fresh produce at the retail level in Malaysia. A total of 152 organic and conventional vegetables were purchased at retail markets in Malaysia. Samples were analyzed for mesophilic aerobic bacteria, yeasts and molds, and total coliforms using conventional microbiological methods. Combination methods of most probable number-multiplex polymerase chain reaction (MPN-mPCR) were used to detect and quantify foodborne pathogens, including Escherichia coli O157:H7, Shiga toxin-producing E. coli (STEC), Listeria monocytogenes, Salmonella Typhimurium, and Salmonella Enteritidis. Results indicated that most types of organic and conventional vegetables possessed similar microbial count (P > 0.05) of mesophilic aerobic bacteria, yeasts and molds, and total coliforms. E. coli O157:H7 and S. Typhimurium were not detected in any sample analyzed in this study. Among the 152 samples tested, only the conventional lettuce and organic carrot were tested positive for STEC and S. Enteritidis, respectively. L. monocytogenes were more frequently detected in both organic (9.1%) and conventional vegetables (2.7%) as compared to E. coli O157:H7, S. Typhimurium, and S. Enteritidis. Overall, no trend was shown that either organically or conventionally grown vegetables have posed greater microbiological risks. These findings indicated that one particular type of farming practices would not affect the microbiological profiles of fresh produce. Therefore, regardless of farming methods, all vegetables should be subjected to appropriate post-harvest handling practices from farm to fork to ensure the quality and safety of the fresh produce.

Enhanced growth and bioconversion of isoflavones in prebiotic-soymilk fermented by UV-treated lactobacilli and bifidobacteria

The aim of this study was to evaluate the effects of ultraviolet (UV) radiation (ultraviolet A (UVA), ultraviolet B (UVB) and ultraviolet C (UVC) at 30–90 J/m2) on the membrane properties of lactobacilli and bifidobacteria, and their bioconversion of isoflavones in prebiotic-soymilk. UV treatment caused membrane permeabilization and alteration at the acyl chain, polar head and interface region of membrane bilayers via lipid peroxidation. Such alteration subsequently led to decreased (p < 0.05) viability of lactobacilli and bifidobacteria immediately after the treatment. However, the effect was transient where cells treated with UV, particularly UVA, grew better in prebiotic-soymilk than the control upon fermentation at 37°C for 24 h (p < 0.05). In addition, UV treatment also increased (p < 0.05) the intracellular and extracellular β-glucosidase activity of lactobacilli and bifidobacteria. This was accompanied by an increased (p < 0.05) bioconversion of glucosides to bioactive aglycones in prebiotic-soymilk. Our present study illustrated that treatment of lactobacilli and bifidobacteria with UV could develop a fermented prebiotic-soymilk with enhanced bioactivity.

Fermented Soymilk as a Nutraceutical

The increasing health awareness and public interest in nutraceuticals and functional foods are growing tremendously, driven along with the continuous efforts of scientific researches in proving and identifying the properties and potential applications of nutraceutical substances. Nutraceuticals are reported as active natural compounds possessing chemoprotective, antioxidative, anti-inflammatory, and osteogenetic properties, which could be obtained from food or being part of a food. Soy contains phytochemicals such as isoflavones and phytosterols that promote health. Soymilk is considered as an economical substitute for dairy and an ideal nutritional supplement for vegan and lactose-intolerant population. The nutritional content of soymilk supports the growth of beneficial microbes, while the fermentation process enriches the medium with various bioactive components. Fermentation improves the bioavailability of isoflavones, assists in digestion of protein, reduces anti-nutritional factor, enhances calcium solubility and vitamin content, promotes intestinal health, and supports immune system. Fermentation of soymilk has indeed offered the population a nutraceutical with physiological benefits and/or provides protection against diseases such as cardiovascular disease, bone health, anticancer, obesity treatment, and antidiabetic property. This health potential has granted fermented soymilk to be positioned as a nutraceutical.