Formation of ethyl ferulate by rice koji enzyme in sake and mirin mash conditions

Carbon stable isotopes of glucose during the degradation of rice by the koji fungus Aspergillus oryzae

Glucose, a key component of traditional Japanese fermented foods, is derived from rice starch via saccharification by hydrolytic enzymes produced by Aspergillus oryzae. The δ 13C value of glucose reflects that of its rice source. However, the influence of saccharification parameters (glucose concentration, degradation temperature, and reaction time) on glucose δ 13C values is unclear. Here, we investigated the influence of saccharification on the δ 13C value of glucose. Our experiments showed a significant difference in the δ 1³C value of glucose (-27.0 ± 0.1 ‰) obtained from saccharification compared to the ingredient rice (-27.1 ± 0.1 ‰) and remaining solid residue (-27.1 ± 0.1 ‰); however, it did not differ significantly from those of rice koji (-27.0 ± 0.1 ‰) and steamed rice (-27.1 ± 0.1 ‰), despite all values being within 0.1 ‰. Notably, glucose concentration, degradation temperature, and reaction time did not significantly affect glucose δ 13C values. These findings demonstrate the remarkable preservation of glucose δ 13C values. The δ 13C values remain aligned with the original δ 13C value of the rice, even with up to 60 % degradation during A. oryzae saccharification. This persistence of the δ 13C value throughout the process offers a potential tool for authenticating the origin of rice-fermented beverages based on the δ 13C value of their glucose component.

Rice used for Japanese sake making

Sake is a Japanese traditional alcoholic beverage made from rice and water. Recently, its export and its production in countries other than Japan have increased. In accordance, both the breeding and the cultivation of sake rice varieties have been extended to wide areas of Japan. To breed new sake rice cultivars and to cultivate rice with high suitability for sake production, an understanding of the properties of the ingredient rice grains and the factors affecting sake making is important. The influence of various rice properties, such as starch structure, protein, water absorption, and grain polishing, on sake making are being revealed in detail. In this review, the properties of rice used for sake making are summarized in terms of fermentation science and rice cultivation.

Catalytic alcoholysis of alkaline extracted lignin for the production of aromatic esters over SO42−/ZrO2-ATP

An efficient process for the depolymerization of alkaline extracted lignin (AEL) using attapulgite (ATP)-supported solid catalysts in ethanol was developed in this work. Different ATP-supported catalysts were prepared and used to catalyze the depolymerization of the lignin AEL. The results demonstrated that the addition of ATP-supported catalysts was favorable for controlling the distribution of valuable depolymerization products. The optimal solid catalyst SO₄²⁻/ZrO₂-ATP (Cat 2) exhibited high catalytic activity and selectivity, which showed a 78.6% conversion of AEL and a 29.4% selectivity to ethyl ferulate (ethyl 4-hydroxy-3-methoxycinnamate) with a catalyst/AEL ratio of 1 : 1 at 200 °C for 120 min. The catalyst could be reused and its catalytic activity did not obviously decreased after 6 successive runs. Particularly, a plausible mechanism involving esterification, hydrogenation, and dehydration for the production of aromatic esters from AEL depolymerization over SO₄²⁻/ZrO₂-ATP in ethanol was also proposed.

An efficient process for the depolymerization of alkaline extracted lignin (AEL) using attapulgite (ATP)-supported solid catalysts in ethanol was developed in this work.

Formation of ethyl ferulate from feruloylated oligosaccharide by transesterification of rice koji enzyme under sake mash conditions

Formation of ethyl ferulate (EF) and ferulic acid (FA) under sake mash conditions was studied using feruloylated oligosaccharide (FO), prepared from rice grains, as the substrate for rice koji enzyme. EF and FA were produced from FO over six times faster than from alkyl ferulates however, under the same ethanol concentration, only small differences were observed between the EF/FA ratios when either FO or methyl ferulate were used as substrates. Esterification and hydrolysis of FO or methyl ferulate showed similar pH dependencies and similar EF/FA ratios for each substrate in all of the pH ranges tested. Ethanol concentration clearly affected the EF/FA ratio; the ratio increased as ethanol concentration increased. Formation of EF and FA in the sake mash simulated rice digest was accelerated by addition of exogenous FO. These results indicated that supply of FO to sake mash is a crucial step for EF and FA formation, and ethanol is an influencing factor in the EF/FA ratio. The rice koji enzyme reaction suggested that EF and FA are formed through a common feruloylated enzyme intermediate complex by transesterification or hydrolysis, and these reactions occur competitively.