The potential synergistic behaviour of inter- and intra-genus probiotic combinations in the pattern and rate of short chain fatty acids formation during fibre fermentation.

This study compared the rate of short chain fatty acid (SCFA) production by different probiotic combinations of Lactobacillus and Bifidobacterium to determine any synergistic effects. Six different fibre fractions were fermented with nine combinations of Lactobacillus rhamnosus (LR), Lactobacillus acidophilus (LA), Bifidobacterium longum (BL) and Bifidobacterium breve (BB) for 0, 6, 24 and 48 h. SCFAs were quantified by gas chromatography. Inter-genus combinations of bacteria produced more SCFA, especially BB + BL + LR, compared to intra-genus that yielded the lowest SCFA production. Acetate was the most abundant, while propionate and butyrate were the most utilised. The SCFA formation was as acetate > propionate > butyrate and the total dietary fibre produced most of the SCFA. Most combinations utilised 60-80% of the fibre; BB + BL + LR digested the fibre completely. The quantity, pattern and the time of release of SCFA depends on the genus, but the combination of pre and probiotics is of great importance for the outcome.

Effect of heat-moisture treatment on digestibility of different cultivars of sweet potato (Ipomea batatas (L.) Lam) starch.

Different heat-moisture levels were applied to native starches from different cultivars of sweet potatoes available in Sri Lanka (Wariyapola red, Wariyapola white, Pallepola variety, Malaysian variety and CARI 273) to study the digestibility level. Samples were treated with 20, 25, and 30% moisture at 85°C and 120°C for 6 h and in vitro starch digestibility was tested with porcine pancreatin enzyme. A range of 19.3-23.5% digestibility was shown by the native starches with no significant difference (P < 0.05). Significant changes were observed in the digestibility level of the hydrothermally modified starches and the moisture content showed a positive impact on the digestibility. Heat-moisture treatment at 85°C brought an overall increase in digestibility and temperature beyond 85°C had a negative impact. No significant difference (P < 0.05) in the digestibility was observed with 20% and 25% moisture at 85°C and increased level were seen at 85°C and 30% moisture.

Effect of Hydroxypropylation on Functional Properties of Different Cultivars of Sweet Potato Starch in Sri Lanka.

Starches obtained from different cultivars of sweet potatoes commonly consumed in Sri Lanka, were chemically modified with hydroxypropyl substitution, to analyze the changes in the physicochemical properties. Significant changes (P < 0.05) in the crude digestibility level, thermal properties, and the water separation (syneresis) of starch gels (7.0% db) during cold and frozen storage were observed due to the modification. Hydroxypropylation increased the gel stability, water solubility, digestibility, and storage stability of the native starches in the cold storage to a significant level. Lowered gelatinization and retrogradation enthalpies as well as gelatinization temperature were observed for derivatized starches compared to the native starch. Low levels of pasting stability with increased levels of breakdown and reduced cold paste viscosity were observed in the hydroxypropylated starch samples except for the Malaysian cultivar (S5). Chemically modified starch gels stored under cold storage did not show a syneresis for two weeks in the cycle and the frozen storage showed much improved stability in the starch gels within the four-week cycle. Chemical modification of sweet potato starch with hydroxyl propyl substitution can enhance the functional characteristics of the native starch which will improve its potential application in the food industry.

Comparative analysis of nutritional quality of five different cultivars of sweet potatoes (Ipomea batatas (L) Lam) in Sri Lanka.

Nutritional attributes of flours obtained from five different cultivars of sweet potato roots commonly available in Sri Lanka showed significant differences in the tested parameters. The starch level ranged between 33% and 64% on the dry basis and the extractability from fresh tubers was governed by the quantity of starch. The crude fiber level ranged between 2.1% and 13.6% on dry basis and the highest level was observed in swp7 (CARI 273) and resistant starch ranged from 14.2% to 17.2%. Higher percentage of resistant starch from total starch was found in Wariyapola red (swp1) cultivar resulting in lower digestion level while higher levels of digestion was evident in cultivars with lower levels of resistant starch with high level of total starch. Low levels of calcium and significant levels of iron were found in the five cultivars studied. Crude protein level was in the range of 1.2-3.3% on dry basis and trypsin inhibitor activity level (TIA) was significantly different (P > 0.05) in the cultivars studied while heating resulted in a significantly high reduction in the TIA level than in unheated condition. Polygonal or round shaped starch granules were in the range of 16.8-23.5 µm and low level of starch digestion was shown in cultivars containing larger granules. Total amylose content lies in the range 15.4-19.6% and cultivars having higher percentage of amylose showed higher level of in vitro pancreatic digestion (Pallepola [swp4] and swp7). The starch digestibility of sweet potato flour was in the range of 36-55% and the highest digestion was observed in swp7. Orange fleshed cultivars (swp4 and swp7) were comparatively rich in nutrients and digestibility than the other three studied cultivars.

Application of Lactobacillus acidophilus (LA 5) strain in fruit-based ice cream.

A study was performed to apply a probiotic strain into fermented ice cream mix with suitable fruit bases to develop a value-added product with a substantial level of viable organisms for a sufficient shelf life. Pure direct vat strain culture of Lactobacillus acidophilus (LA 5) in freeze-dried form was inoculated into a mixture of ice cream, frozen, and the number of viable organisms during frozen storage for a period of time was enumerated, using turbidity measurements with a spectrophotometer. An ice cream sample prepared without the probiotic culture was compared with the test sample for quality, by testing the basic quality parameters for ice cream. Results show a reduction in the over run of the probiotic ice cream compared to the nonprobiotic ice cream. Significantly high level (P < 0.05) of total solids (42%), proteins (16.5%), and titratable acidity (2.2%) was observed in the test sample compared to the nonprobiotic ice cream. Significantly low pH level in the probiotic sample may be due to the lactic acid produced by the probiotic culture. No significant difference (P > 0.05) in the fat content in the two types of ice cream was observed. A significantly low level (P < 0.05) of melting in the probiotic one may have resulted from less over run, than the nonprobiotic sample. Rapid reduction in the viable cells during frozen storage occurred at -18°C and gradual adaptation occurred over the first 4 weeks. At the 10th week, 1.0 × 10(7) numbers of viable organisms were present in 1 g of the probiotic ice cream. Results show the presence of a sufficient number of viable organisms in the product for the 10-week period, which would be beneficial to consumers.

The influence of environmental factors on the adhesion of combinations of probiotics to rice fibre fractions.

Nine co-cultures of the Bifidobacterium and Lactobacillus species were tested for their ability to adhere to insoluble dietary fibre (IDF1, IDF2), soluble dietary fibre (SDF1, SDF2), and total dietary fibre (TDF1, TDF2) from two rice varieties (RR1 and RR2). Combinations of the same genus (BB + BL and LA + LR) showed 30-40 % (poor) adhesion, and combinations of different genera showed 40-50 % (moderate) adhesion, which is significantly higher (p < 0.05) than the combinations of same genus. The increase in adhesion with species from different genera suggests some synergistic activity. The microbial combinations had the ability to adhere to dietary fibre fractions as early as 30 min. Colonization of rice fibre by bacterial cells was affected by the temperature, with adhesion being higher at 37 °C than at room temperature. The optimal pH value for adhesion was 4.2-4.5. This study observed that the combinations tested had a moderate percentage of adhesion in the presence of bile, low pH (4.3-4.5) and pancreatin, irrespective of the type of co-culture. In addition, adhesion was not affected by an increase in NaCl and Tween 80. Adhesion was affected by disaccharides and polysaccharides. The amount of adhesion of co-cultures was not significantly affected by the substrate (p > 0.05). Results indicated that rice fibre fractions are suitable hosts for the probiotics tested.

The effect of rice fibre fractions on the growth of co-cultures of probiotics.

The fermentation of rice dietary fibre was measured by the cell yield, pH, optical density specific growth rate and biomass using nine co-cultures of four probiotics at 0, 6, 24 and 48 h incubation. The results from the fermentation of the soluble, insoluble and total dietary fibre (SDF, IDF, and TDF) of two rice varieties were compared. Overall there was no significant difference (p < 0.05) in the fermentation of the six different rice fibre fractions. However, co-cultures showed a preference for glucose as a fermentation substrate rather than the fibre fractions. Bifidobacteria species produced a higher cell count than the Lactobacillus species after 24 and 48 h of fermentation (p < 0.05). There was evidence of synergistic activity with increased growth observed when lactobacilli and Bifidobacterium were grown together. Growth was limited by the pH reaching 4.2-4.45. Specific growth rates of the co-cultures varied for different culture combinations. Combinations of the same species produced less biomass than combinations of mixed species. Bifidobacterium breve + Bifidobacterium longum + Lactobacillus rhamnosus was the most efficient. These findings showed that synergism between microorganisms in co-cultures affected the degree of fermentation of dietary fibre.