Flavor compounds with high odor activity values (OAV > 1) dominate the aroma of aged Chinese rice wine (Huangjiu) by molecular association

Aging is an essential operation to perfect the flavor quality of Hungjiu. In this study, formation mechanism of flavor compounds responsible for the characteristic flavor of aged Huangjiu was investigated. The contents of umami and bitter free amino acids (FAA) increased with the storage period prolonged, while that of sweet FAA showed downward trend. Gas chromatograph-mass spectrometry and principal component analysis indicated that the volatile flavor compounds with OAV exceed 1, especially middle-chain fatty-acid-ethyl-esters and aromatic compounds, dominated the characteristic flavor of aged Huangjiu. Low field-NMR was firstly applied to characterize the molecular association between water and dissolved flavor compounds in aged Huangjiu. The results showed that basic amino acids contributed greatly to the flavor formation of aged Huangjiu via molecular association. In addition, the molecular association significantly promoted the accumulation of flavor compounds with OAV > 1, especially ethyl esters.

Insights on the role of acetaldehyde and other aldehydes in the odour and tactile nasal perception of red wine

Wine models with or without a dearomatised and lyophilized red wine extract containing a young red aroma base (control) plus one vector with one or several aroma compounds (unsaturated-aldehydes, saturated-aldehydes, benzaldehyde, isoamyl-alcohol, methoxypyrazines and (Z)-1,5-octadien-3-one) were prepared. Models were spiked with increasing amounts of acetaldehyde whose headspace concentrations were controlled. Odour and nasal chemesthesic properties were assessed by a trained sensory panel. Results confirm the contribution of the different players, notably isoamyl-alcohol, (Z)-1,5-octadien-3-one, benzaldehyde and methoxypyrazines, to wine aroma and tactile nasal characteristics and demonstrate that acetaldehyde levels play an outstanding role in their modulation. At low levels, it can play positive roles in some specific aromatic contexts, while at higher levels, enhance the negative effects associated to the generic presence of other aldehydes (saturated, unsaturated and Strecker aldehydes) by enhancing "green vegetable" notes and "itching" character and the "burning" effects linked to high levels of isoamyl alcohol.

Fine tuning of medium chain fatty acids levels increases fruity ester production during alcoholic fermentation

Pichia fermentans Z9Y-3 and its intracellular enzymes were inoculated along with S. cerevisiae in synthetic grape must to modulate fruity ester production. The levels of ester-related enzymes, ester precursors, and fruity esters were monitored every 24 h during fermentation. Results showed that the levels of ethyl acetate, acetate higher alcohol esters (AHEs), short chain fatty acid ethyl esters (SFEs), and medium chain fatty acid ethyl esters (MFEs) were significantly enhanced in mixed fermentation. Pearson correlation analysis further revealed that higher alcohols and fatty acids played a more important role in fruity ester production than enzymes; Particularly, the correlation coefficient between fatty acids and MFEs was 0.940. In addition, supplementation of medium chain fatty acids (7.2 mg/L) at the metaphase of single S. cerevisiae fermentation improved ethyl acetate, AHE, SFE, and MFE production by 42.56%, 21.00%, 61.33%, and 90.04%, respectively, although the high level of ethyl acetate might result in off-flavors.

Effect of a novel Lactobacillus paracasei starter on sourdough bread quality

The novel Lactobacillus paracasei K5 strain, recently isolated from Greek cheese, was evaluated as potential sourdough bread starter. Breads were made using different amounts of L. paracasei sourdoughs as well as traditional sourdough for comparison. Quality characteristics of the breads (acidity and rising) were examined, as well as rope spoilage through macroscopic observations and molecular analysis (PCR-DGGE). The highest acidity levels (3.15 g lactic acid and 1.13 g acetic acid per kg of bread) and better resistance to rope spoilage were observed when bread contained 30% w/w L. paracasei K5 sourdough. Spoilage in the L. paracasei K5 breads was observed at 15-16 days, 5 days later than the control breads. In addition, L. paracasei K5 sourdough improved the bread sensory properties, as reflected by consumer preference and GC/MS analysis of aroma volatiles. Therefore, L. paracasei K5 can be successfully used for sourdough bread making with good quality and extended shelf-life.