Influence of physical and chemical modifications on granule size frequency distribution, fourier transform infrared (FTIR) spectra and adsorption isotherms of starch from four yam (Dioscorea spp.) cultivars.

Abstract: In this work, the effect of the modifications (annealing, acid hydrolysis and citric acid substitution) on starch granule size frequency distribution, Fourier Transform Infrared (FTIR) spectra, and adsorption isotherm of starches of four yam cultivars were studied. The native and modified white yam, water yam, and yellow yam starches had a normal distribution frequency profile for the granule sizes, which were similar among the cultivars. In contrast, the native and modified bitter yam starch granules were not normally distributed. The modifications resulted in a left shift in normal distribution frequency profiles for the granules sizes of the white, water and yellow yam starches due to broadening of the range of granule sizes. The FTIR spectra revealed that additional bands at 1726.95-1729.49 cm-1 were introduced due to citric acid modification of the yam starches. The modifications also caused weakening of the FTIR band representing -CH2 and -OH stretching at 2927.85-2932.94 cm-1 and 3259.42-3437.33 cm-1, respectively. The native, annealed and acid hydrolyzed yam starches all had similar adsorption isotherms at 28 °C. On the other hand, the citric acid-substituted yam starches showed a different adsorption isotherm, because they had significantly higher equilibrium moisture content at water activity (a w ) above 0.9. All the adsorption isotherms were type III, J-shaped isotherms. The adsorption isotherms data of the yam starches fitted best to the Guggenheim-Anderson-De Boer (GAB) model. The GAB model monomolecular moisture content ranged between 0.0165 and 0.0597 g/g db. Article Highlights: Native and modified yam starches' granules size were normally distributed except bitter yam starchFTIR revealed additional bands and molecular rearrangements were introduced due to modificationsAdsorption isotherms revealed type III, GAB-model isotherms with low monomolecular moisture. Supplementary Information: The online version contains supplementary material available at 10.1007/s13197-021-05200-7.

Physical, chemical and adsorption isotherm characteristics of fermented soybean cultivars, and cracked and dehulled African locust bean using selected Bacillus spp.

Physical, chemical and adsorption isotherm characteristics of fermented soybean cultivars and dehulled African locust bean using selected Bacillus spp. were investigated. The CIE Lab, pH, titratable acidity, temperature and viable cells of the fermented cotyledons count increased significantly (p < 0.05) during the 5 days fermentation period. The CIE (Lab) varied with method of dehulling of cotyledons prior to and during fermentation, drying and milling. Protein content of African locust bean (25.50-40.25%) and soybean (40.15-50.60%) increased, but carbohydrate content reduced during fermentation of African locust bean (30.20-15.08%) and soybeans (18.21-12.08%). Adsorption isotherm patterns of the dried and milled African locust bean and soybean cultivars were sigmoidal. Of the eight models used, the BET and GAB models gave good fit, with a good correlation coefficient (0.95-0.76) and low average (81.93-14.82). The GAB had better fit, greater relevance and theoretical significance when compared with other models. Cracking to remove cotyledons from locust beans prior to fermentation yielded condiment with better aesthetic appeal and nutritional qualities than the traditional cooking for extensive period used for dehulling and softening of African locust bean seeds.

Extrusion processing of raw food materials and by-products: A review.

Extrusion technology has rapidly transformed the food industry with its numerous advantages over other processing methods. It offers a platform for processing different products from various food groups by modifying minor or major ingredients and processing conditions. Although cereals occupy a large portion of the extruded foods market, several other types of raw materials have been used. Extrusion processing of various food groups, including cereals and pseudo cereals, roots and tubers, pulses and oilseeds, fruits and vegetables, and animal products, as well as structural and nutritional changes in these food matrices are reviewed. Value addition by extrusion to food processing wastes and by-products from fruits and vegetables, dairy, meat and seafood, cereals and residues from starch, syrup and alcohol production, and oilseed processing are also discussed. Extrusion presents an economical technology for incorporating food processing residues and by-products back into the food stream. In contemporary scenarios, rising demand for extruded products with functional ingredients, attributed to evolving lifestyles and preferences, have led to innovations in the form, texture, color and content of extruded products. Information presented in this review would be of importance to processors and researchers as they seek to enhance nutritional quality and delivery of extruded products.

Effects of tempering (annealing), acid hydrolysis, low-citric acid substitution on chemical and physicochemical properties of starches of four yam (Dioscorea spp.) cultivars.

The effects of tempering (annealing), acid hydrolysis and low-citric acid substitution on chemical and physicochemical properties of starches of four Nigerian yam cultivars were investigated. Crude fat and protein contents of the native starches decreased significantly after the modifications, while nitrogen-free extract increased significantly with acid hydrolysis and citric acid substitution. Acid hydrolysis and low-citric acid substitution reduced the least concentration for gel formation of the starches from 4 to 2% w/v, but tempering had no effect. Swelling power of the starches reduced significantly, and water solubility increased significantly at 75 and 85 °C, especially with acid hydrolysis and low-citric acid substitution. However, tempering significantly reduced starch solubility in the four cultivars. Paste clarity of starches of white (29.17%), water (18.90%), yellow (30.90%) and bitter (10.57%) yams reduced significantly with tempering to 14.43, 11.83, 16.93 and 7.27%, but increased significantly with acid hydrolysis to 41.40, 35.37, 28.77 and 32.33%, and low-citric acid substitution to 36.60, 44.17, 50.67 and 14.33%, respectively. Pasting properties such as peak, trough, breakdown, final, and setback viscosities and peak time of native starches reduced significantly with acid hydrolysis and low-citric acid substitution, however, tempering significantly increased their pasting temperature, peak time, setback and final viscosities.

Physico-chemical, sensory and microbiological characteristics of plain yoghurt from bambara groundnut (Vigna subterranea) and soybeans (Glycine max).

Physico-chemical, sensory and microbiological characteristics of plain yoghurt from bambara groundnut and soybean milks were studied. Milks were prepared from bambara and soybean and then fermented using Lactobacillus delbruieckii subspp. bulgaricus and Streptococcus salivarus subspp. thermophilus to produce yoghurt. The yoghurts were stored at 7 °C and 27 °C for 9 days and their quality monitored. Results showed that pH of soy and bambara yoghurts decreased during the storage period for both storage temperatures. This decrease in pH was accompanied by simultaneous increase in titratable acidity. Total solids and apparent viscosities of soy and bambara yoghurts increased at 7 °C, but decreased at 27 °C during storage period. Bambara yoghurt received higher sensory acceptability than soy yoghurt. Predominant microorganisms in the stored yoghurts were lactic acid bacteria (LAB). The LAB count in the yoghurts stored at 7 °C decreased but increased at 27 °C during the storage period. Similar trends were followed by total aerobic bacteria, yeast and moulds counts. Pathogenic bacteria such as Salmonella, Coliform and E. coli were absent in all the yogurt samples. Yoghurts of acceptable quality and safety were produced from bambara groundnut and soybeans.

Physical, functional, and pasting properties of flours from corms of two Cocoyam (Colocasia esculenta and Xanthosoma sagittifolium) cultivars.

Physical, functional and physicochemical properties of flours of five cocoyam (Colocasia spp and Xanthosoma spp) cultivars were evaluated. Colour (L*a*b*) parameters of corms and flours, pasting and functional properties of the flours were determined. Xanthosoma spp showed significantly higher length (95.16-151.46), width (75.29-78.03) and weight (179.20-605.94) than the Colocasia spp., but the parameters did not vary significantly within either Xanthosoma and Colocasia spp. Generally, colour of peeled corms [L* (72.08-78.93); a* (+1.06 - +3.5); b* (+17.65 - +35.80)] was lighter than the flours [L* (69.35-84.97); a* (+0.30 - + 4.76); b* (+4.44 - +23.48)]. The NXs001 showed significantly higher peak (201.71RVU), trough (186.75 RVU), final (289.75 RVU) and setback (103 RVU) viscosities that the other cultivars. Pasting profiles of the cocoyam flours showed similar trend with the NXs001 showing a steeper curve. Pasting temperature and peak time ranged from 87.33 to 92.53 °C and 5.17-6.34 min, respectively. Water absorption capacity, gelling point, pH, foam capacity, bulk density and swelling power varied from 32-69 %, 6.56-7.59, 58.5-72.5 °C, 7.19-14.72 %, 0.94-1.01 g/mL and 3.18-7.36, respectively.

Effect of sucrose and binary solution on osmotic dehydration of bell pepper (chilli) (Capsicum spp.) varieties.

Pepper (chilli) (Capsicum annum) varieties, 'Tatase' and 'Rodo', (Capsicum frutescens) 'Sombo' and 'Bawa' were osmotically dehydrated in sucrose solutions of 40, 50 and 60o Brix and binary solutions of 50° sucrose with 5, 10 and 15% salt at 20, 30 and 40°C for 9 h. Samples osmosed at higher sugar concentrations (50° and 60°Brix) gave better results while improved solute gain were obtained using binary mixture with lower processing time, energy and cost. Effects of varietal differences on solid gain and water loss showed a descending in the order 'Sombo', 'Rodo', 'Bawa' and 'Tatase'. The colours were retained and stabilized after osmotic dehydration. Therefore, the solid gain and colour retention are indications of value addition.