Effect of enzymatic hydrolysis on digestibility and morpho-structural properties of hydrothermally pre-treated red rice starch.

The objective of this work was to evaluate the effects of enzymatic hydrolysis on digestibility and morphological and structural properties of hydrothermally pre-treated (HPT) red rice starch. The pre-treatments were performed in autoclave and cooking for the modification of rice grains and native starch. In vitro starch digestibility was performed consecutively and semi-simultaneously using α-amylase and amyloglucosidase. A first-order mathematical model was used to adjust the hydrolysis kinetic data, which made it possible to calculate the surface area, hydrolysis index, and glycemic index of the starch. Scanning electron microscopy images (SEM), Fourier transform infrared (FTIR) spectra and X-ray diffraction (XRD) were also performed to investigate the characteristics of the post-hydrolysis starch samples. The autoclaved starch HSS-A3, which was subjected to 121 °C/1.08 bar for 10 min, showed the highest in vitro digestibility values (80.08 %). Both starch samples showed increase of particle size and enzymatic digestibility after HPT. FTIR spectra of the starch samples showed that there was no appearance of new functional groups. However, XRD evidenced that HPT changed the intensity of the peaks and the type of crystallinity was changed for autoclaved starch (A3) from type A to Vh, with crystallinity ranging from 21.71 % to 26.42 %. The semi-simultaneous approach showed more advantages due to the highest in vitro digestibility as well as reducing the processing time and use of reagents.

Potential of "coalho" cheese whey as lactose source for ß-galactosidase and ethanol co-production by Kluyveromyces spp. yeasts.

The present study evaluated the co-production of ß-galactosidase and ethanol by Kluyveromyces marxianus ATCC 36907 and Kluyveromyces lactis NRRL Y-8279 using as carbon source the lactose found on "coalho" cheese whey. Cheese whey was subjected to partial deproteinization, and physicochemical parameters were assessed. Cultivations were carried out in an shaker to evaluate two carbon/nitrogen (C:N) ratios. The best C:N ratio (1.5:1) was carried to 1.5-L bioreactor cultivation in order to increase co-production yields. The stability of ß-galactosidase was assessed against different temperatures and pH, and in the presence of metal ions. Concerning the co-production of ß-galactosidase and ethanol, K. lactis proved to be more efficient in both the C:N ratios, reaching 21.09 U·mL-1 of activity and 7.10 g·L-1 of ethanol in 16 h. This study describes the development of a viable and value-adding biotechnological process using a regional cheese by-product from Northeast Brazil for co-production of biomolecules of industrial interest.