A Novel Approach to Develop Lager Yeast with Higher NADH Availability to Improve the Flavor Stability of Industrial Beer

Flavor stability is important for beer quality and extensive efforts have been undertaken to improve this. In our previous work, we proved a concept whereby metabolic engineering lager yeast with increased cellular nicotinamide adenine dinucleotide hydride (NADH) availability could enhance the flavor stability of beer. However, the method for breeding non-genetically modified strains with higher NADH levels remains unsolved. In the current study, we reported a novel approach to develop such strains based on atmospheric and room temperature plasma (ARTP) mutagenesis coupled with 2,4-dinitrophenol (DNP) selection. As a result, we obtained a serial of strains with higher NADH levels as well as improved flavor stability. For screening an optimal strain with industrial application potential, we examined the other fermentation characteristics of the mutants and ultimately obtained the optimal strain, YDR-63. The overall fermentation performance of the strain YDR-63 in pilot-scale fermentation was similar to that of the parental strain YJ-002, but the acetaldehyde production was decreased by 53.7% and the resistance staling value of beer was improved by 99.8%. The forced beer aging assay further demonstrated that the favor stability was indeed improved as the contents of 5-hydroxymethylfurfural in YDR-63 was less than that in YJ-002 and the sensory notes of staling was weaker in YDR-63. We also employed this novel approach to another industrial strain, M14, and succeeded in improving its flavor stability. All the findings demonstrated the efficiency and versatility of this new approach in developing strains with improved flavor stability for the beer industry.

Effects of Storage Conditions on the Flavor Stability of Fried Pepper (Zanthoxylum bungeanum) Oil

Flavor stability of fried pepper oil was investigated during 30 days of storage. Variation trends of key volatile flavor compounds in fried pepper oil induced by ultraviolet (UV) irradiation and oxygen (O2) exposure were compared using GC-MS and chiral GC-MS analysis. Chirality analysis showed that conversion of (S)-(-)-limonene to (R)-(+)-limonene form was observed during storage. The storage conditions did not change the configuration of linalool, linalool oxide, or carvone. Quantitative analysis showed that the concentrations of linalool, limonene, 1,8-cineole, β-myrcene, and β-ocimene decreased dramatically during storage, whereas carvone, (E)-2-heptenal, and linalool oxide showed an increasing trend during storage. The loss rate of limonene and linalool exhibited the highest under combined UV and O2 condition, which played an important role for the aroma attenuation of pepper oil. This result will benefit the storage of pepper oil and based on pepper oil aromatic products.

Impact of Dry Hopping on Beer Flavor Stability

To investigate the chemical and sensorial impact of dry hopping time on typical pale ale, a standardized beer was produced and separated into ten vessels. Nine vessels were dry hopped, and one vessel remained un-hopped as a control. Impact of dry hopping contact time was investigated over 96 h. Polyphenols and iso-α-acid t/c ratio were analyzed in both Young and Aged beer samples. Total polyphenol content generally increased in both young and aged treatments compared to controls. Analysis of the t/c ratio suggests that both Young and Aged beers were chemically preserved to some degree after approximately 12 h at the given dry hopping rate regardless of age. Within the Aged beer trials, 96 h of dry hop contact yielded a significant increase in t/c ratio compared to all other Aged trials. This suggests that a 4-day dry hop regime may yield additional oxidative protection of iso-α-acids in beers stored unrefrigerated for 30 days. Descriptive analysis was also performed with an 8-person, trained panel; however, beers were sensorially distinguished by their aging time as opposed to their dry hopping time.

Optimization of wall components for encapsulation of Nigella sativa seed oil by freeze-drying

The aim of the present study was to determine the proper concentrations of whey protein isolate (WPI), Arabic gum (AG), and Zedo gum (ZG) for the encapsulation of Nigella sativa seed oil (NSO). WPI, AG, and ZG were used as wall materials for the encapsulation of NSO by mixture design and then the optimum sample with minimum Z-average, PDI, and a* and maximum zeta potential, conductivity, encapsulation efficiency, and b* was selected for examining FT-IR and SEM. The findings demonstrated that lower particle size and particle dispersion index were obtained at higher amounts of AG and WPI with the least a*. Desirability function results indicate that the mixture of 39.05% WPI, 16.758% AG, and 4.192% ZG led to the production of the optimum sample. Microencapsulation of Nigella sativa seed oil using the optimum wall composition was recognized to be useful to preserve bioactive compounds and provide flavor stability, enabling the use of microcapsules in food formulations.

Physico-Chemical and Sensory Qualities of Ice Cream Incorporated with Encapsulated Flavour

Flavour is the most important positive attribute in ice cream. However its stability in ice cream during processing and storage get decreased. In order to limit its degradation in ice cream during processing and storage it is beneficial to encapsulate flavor compounds. The aim of this study is to evaluate flavor encapsulated (FE 1 and FE 2) compounds, physico-chemical of different flavor encapsulated ice cream (FEIC 0, FEIC 1, FEIC 2) and sensory qualities of different flavor encapsulated ice cream on different days ( 0 day, 7thd day and 15th day). The ice cream were prepared with 1.35 % of FE 1 and FE 2 in ice cream and were analyzed for physico-chemical and sensory qualities and compared with regular ice cream (control – FEIC 0). The result of the present study shows that shape of the aggregated encapsulated flavour were irregular, but it is spherical in shape when it is dispersed. The size of the aggregated FE 1 and FE 2 did not differ significantly, but size of the dispersed and solubility of different encapsulated flavor differed significantly ( 0.01). Among physico-chemical properties, ice cream incorporated with encapsulated flavour significantly increased ( 0.05) viscosity and melting resistance of the ice cream, but it has not having any influence on pH, titratable acidity (%), fat (%), total solid (%) and specific gravity when compared with control ice cream (FEIC 0). In sensory qualities, colour and appearance of different flavour encapsulated ice cream did not differ significantly on different storage period. The intensity of flavour was significantly higher ( 0.01) in FEIC 0 on 0th day and non-significant among treatments on 7th day. But on 15th day the intensity of flavour was significantly higher in FEIC 1 and FEIC 2 when compared with FEIC 0 were analyzed using sensory panelist. Thus the study revealed that incorporation of FE compound in ice cream improves flavor stability in ice cream without affecting much of its physico-chemical properties.

Impact of temperature and water activity on the aroma composition and flavor stability of pea (Pisum sativum) protein isolates during storage

Flavor stability of pea protein isolates (PPIs) during storage was investigated.