Improvement of in vitro digestibility and thermostability of debranched waxy maize starch by sequential ethanol fractionation.

This study aimed to improve the in vitro digestibility and thermostability of debranched waxy maize starch (DWMS) by sequential fractionation. Waxy maize starch was debranched by pullulanase, followed by sequential precipitation through controlling the ratio of starch supernatants to ethanol at 1:0.5, 1:1, and 1:1.5 (v/v). Subsequently the structural, thermal, in vitro digestive properties of DWMS were investigated. In vitro digestion results showed that the secondary ethanol fractionation of 1:1 on the basis of the initial fractionation (1:0.5) induced a significant higher amount of slowly digestive starch (SDS, 30.0 %) and resistant starch (RS, 58.6 %) amongst all three fractions, along with the highest peak temperature (Tp, 106.4 °C) and the highest decomposition value (Td, 310.0 °C) in calorimetric (DSC) and thermogravimetry (TGA) measurements. Chain length distribution, surface morphology, and laser confocal micro-Raman spectroscopy (LCM-Raman) analyses revealed that medium (degree of polymerization, DP 13- 36) and long chains (DP ≥37) respectively constituting 72.0 % and 10.2 % of DWMS resulted in the formation of spheroidal crystallites with higher homogeneity and more ordered short-range structures. Overall, this work confirmed that ethanol fractionation is an efficient method for improving the in vitro digestibility and heat stability of waxy maize starch.

Effect of fat concentration on protein digestibility of Chinese sausage.

Chinese sausage is a popular traditional Chinese meat product, but its high-fat content makes consumers hesitant. The purpose of this study is to compare the nutritional differences of Chinese sausages with different fermentation times (0, 10, 20, 30 d) and fat content (the initial content was 11.59% and 20.14%) during digestion. The comparison of digestion degree, protein structure, and peptide composition between different sausages were studied through in vitro simulated digestion. Chinese sausages with high-fat content had higher α-helix, ß-turn, and random coil, making them easier to digest. The fermentation process made this phenomenon more pronounced. The high-fat sausage fermented for 10 d showed the highest release of primary amino acids (about 9.5%), which was about 3.5% higher than the low-fat sausage under the same conditions. The results of peptidomics confirmed the relevant conclusions. After gastric digestion, the types of peptides in the digestive fluid of high-fat sausages were generally more than those in low-fat sausages, while after intestinal digestion, the opposite results were observed. The type of peptide reached its peak after fermentation for 20 d. These findings are of obvious significance for selecting the appropriate fermentation time and fat content of Chinese sausages.

Flavor evolution of normal- and low-fat Chinese sausage during natural fermentation.

This work compared the flavor evolution of normal-fat (NF) with that of low-fat (LF) Chinese sausage during natural fermentation. Higher degree of lipid oxidation occurred in NF sausages, resulting in its faster formation of stable volatile profiles. Faster formation of esters occurred in NF sausage in the initial 10 days, whereas prolonged fermentation reduced the level of ethyl lactate-M, ethyl heptanoate, ethyl hexanoate-D and ethyl pentanoate-D. Gradual reduction of alcohols was observed in both groups, and surge in aldehydes occurred in LF samples during day 20-30 period. Faster formation of taste characteristics and larger amount of 2-methylfuran as well as 2,3-dimethylpyrazine were found in LF sausages, since more free amino acids were liberated in LF sausages. Umami and aftertaste tastes formed in the first 20 days, whereas prolonged fermentation reduced these favorable taste. These results highlight that the choice of proper fermentation duration should largely depend on the fat content in Chinese sausages.