Banana starch modified by heat moisture treatment and annealing: Study on digestion kinetics and enzyme affinity.

Starch modification by annealing (ANN) and heat-moisture treatment (HMT) results in a lower crystallinity compared to native but the change of B crystalline type to A type is only observed in HMT starch. All starches possess two different digestion rate constants i.e. k1 (at rapid phase) and k2 (at slow phase) which may be linked to the preserved intact starch granule following thermal treatment. HMT starch contains higher content of slowly digestible starch (C2∞) compared to the C2∞ of the other starches. The lower enzyme binding to HMT starch (Kd value increases from 0.12 mg/mL in native starch to 0.83 mg/mL) may be linked to the increase in the degree of ordered structure of the granule surface (observed from the absorption band ratio of 1000 cm-1/1022 cm-1). The lower affinity may lead to a lower k1 value. This holds true for ANN and native starch which displays similar k1, Kd value and degree of ordered to disordered structure. Lower k2 in HMT starch compared to the corresponding k2 in the other starches may be linked to the slower enzyme diffusion into the core of starch granule due to the tightly packed structure of A crystalline type in HMT starch.

Potential Application of Yeast Cell Wall Biopolymers as Probiotic Encapsulants.

Biopolymers of yeast cell walls, such as ß-glucan, mannoprotein, and chitin, may serve as viable encapsulants for probiotics. Due to its thermal stability, ß-glucan is a suitable cryoprotectant for probiotic microorganisms during freeze-drying. Mannoprotein has been shown to increase the adhesion of probiotic microorganisms to intestinal epithelial cells. Typically, chitin is utilized in the form of its derivatives, particularly chitosan, which is derived via deacetylation. Brewery waste has shown potential as a source of ß-glucan that can be optimally extracted through thermolysis and sonication to yield up to 14% ß-glucan, which can then be processed with protease and spray drying to achieve utmost purity. While laminarinase and sodium deodecyle sulfate were used to isolate and extract mannoproteins and glucanase was used to purify them, hexadecyltrimethylammonium bromide precipitation was used to improve the amount of purified mannoproteins to 7.25 percent. The maximum chitin yield of 2.4% was attained by continuing the acid-alkali reaction procedure, which was then followed by dialysis and lyophilization. Separation and purification of yeast cell wall biopolymers via diethylaminoethyl (DEAE) anion exchange chromatography can be used to increase the purity of ß-glucan, whose purity in turn can also be increased using concanavalin-A chromatography based on the glucan/mannan ratio. In the meantime, mannoproteins can be purified via affinity chromatography that can be combined with zymolase treatment. Then, dialysis can be continued to obtain chitin with high purity. ß-glucans, mannoproteins, and chitosan-derived yeast cell walls have been shown to promote the survival of probiotic microorganisms in the digestive tract. In addition, the prebiotic activity of ß-glucans and mannoproteins can combine with microorganisms to form synbiotics.

Antifungal and Aflatoxin-Reducing Activity of ß-Glucan Isolated from Pichia norvegensis Grown on Tofu Wastewater.

Yeast can be isolated from tofu wastewater and the cell wall in the form of ß-glucan can act as a natural decontaminant agent. This study aimed to isolate and characterize native yeast from tofu wastewater, which can be extracted to obtain ß-glucan and then identify the yeast and its ß-glucan activity regarding antifungal ability against Aspergillus flavus and aflatoxin-reducing activity towards aflatoxin B1 (AFB1) and B2 (AFB2). Tofu wastewater native yeast was molecularly identified, and the growth observed based on optical density for 96 h and the pH also measured. ß-glucan was extracted from native yeast cell walls with the acid-base method and then the inhibition activity towards A. flavus was tested using the well diffusion method and microscopic observation. AFB1 and AFB2 reduction were identified using HPLC LC-MS/MS. The results showed that the native yeast isolated was Pichia norvegensis with a ß-glucan yield of 6.59%. Pichia norvegensis and its ß-glucan showed an inhibition zone against Aspergillus flavus of 11.33 ± 4.93 and 7.33 ± 3.51 mm, respectively. Total aflatoxin-reducing activity was also shown by Pichia norvegensis of 26.85 ± 2.87%, and ß-glucan of 27.30 ± 1.49%, while AFB1- and AFB2-reducing activity by Pichia norvegensis was 36.97 ± 3.07% and 27.13 ± 1.69%, and ß-glucan was 27.13 ± 1.69% and 32.59 ± 4.20%, respectively.

Non-starch contents affect the susceptibility of banana starch and flour to ozonation.

The properties of native flour and starch were compared and the changes in their properties were evaluated following ozonation at 100 and 200 ppm. X-ray diffraction analysis indicated that crystallinity index of both ozonated banana flour and starch decreased by 1.6%, B-type pattern of native banana flour and starch did not change following ozonation. The presence of higher amounts of non-starch components decreased the sensitivity of flour to the oxidation, as indicated by the lower carboxyl content compared to that of starch. The flour also required higher ozone concentration than starch to alter its properties, particularly pasting properties. Ozonation tended to increase peak, hold and final viscosity of both. A prominent change in the freeze thaw stability of both flour and starch following ozonation was the most encouraging result. Ozonation also improved the solubility of flour which was important to reduce cooking loss when applied in a range of food products. The solubility improvement in the flour might be linked to the formation of new binding following ozonation presumably involving protein present in the granule surface.