Beer is a microbiologically stable beverage due to several inhibitory factors for microbial growth. In fact, only a restricted number of species can grow in and spoil beer. The vast majority of beer spoilage microorganisms are lactic acid bacteria belonging to the genera Lactobacillus and Pediococcus. However, many beer spoilage microorganisms exhibit extremely poor culturability, and they are hard to detect by the conventional laboratory media adopted for the quality control of beer. This often leads to quality incidents without the detection of the causative agents in breweries. In addition, the continual emergence of new beer spoilage species has been problematic for brewers that traditionally depend on species identification methods for quality control in the brewing processes. To overcome these difficulties, the brewing industry has strived to develop new microbiological media and species-independent methods for comprehensively detecting and identifying beer spoilage microorganisms. Some brewers are now evaluating new techniques, including inexpensive third-generation DNA sequencing, for the comprehensive identification of beer spoilage microorganisms and hygiene indicators. In this review, the recent progress of microbiological quality control methods in unpasteurized beer production is summarized.
To easily evaluate the in-mouth release characteristics of beverage odorants from the viewpoint of release rate, the quantitative value ratio (dividing the quantitative value for 10 breaths by that for the first breath) was calculated using the Retronasal Flavor Impression Screening System (R-FISS) for odorants contained in retronasal aroma after drinking. It was expected that this ratio would be large for odorants released slowly and small for odorants released rapidly. The quantitative value ratio for odorants contained in the retronasal aroma when drinking a coffee beverage calculated by the R-FISS had a unique value for each odorant. Odorants with a small quantitative value ratio (sulfur-containing compounds with a roasty note) may be released in a short time, while odorants with a large quantitative value ratio (pyrazines with a nutty note, phenols with a smoky note) may be continuously released over a long period of time. Therefore, as a result of examining the relationship between the quantitative value ratio in the R-FISS and the time change of the retronasal aroma by real-time measurement, it was found that the concentration of odorants with a small quantitative value ratio decreased quickly after drinking and odorants with a large quantitative value tended to maintain a constant concentration for a long time after drinking. Furthermore, a sensory evaluation by the Temporal Dominance of Sensations (TDS) method indicated that the retronasal aroma felt after drinking changed from a roasty note to a nutty, smoky note over time. These findings indicate that the quantitative ratio in the R-FISS can be applied to estimate the in-mouth release characteristics (release rate) for each odorant in beverages.
Herein, proton quantitative nuclear magnetic resonance (1H qNMR), an absolute quantification method, was used to identify the types of glycosidic bonds contained in glucans and to quantify them individually. In this study, glucan quantities were determined using signals arising from an anomeric proton of the glucose unit, which showed a signal at δ 4.2 to 5.3 ppm and was well separated from the other signals. The signal area derived from the anomeric proton in the major α- and β-glucans measured by 1H qNMR exhibited good linearity (r＝0.999) in a sample concentration range of 0.1 to 2 w/v %. 1H qNMR correctly fulfilled the conditions of purity of β-glucan standards obtained from barley and baker’s yeast, with an accuracy of within 1 %. Furthermore, the quantity of glucans in dietary supplements determined by 1H qNMR was largely consistent with the quantitative value obtained by a conventional method employed to determine glucose generated from glucans by sulfate hydrolysis. 1H qNMR enabled non-destructive quantification of glucans, and was particularly effective for glucans consisting of a single unbranched glycosidic bond, such as pustulan and curdlan.
The firmness and components of potato were preliminarily modified by freeze-thaw impregnation with macerating enzymes and emulsified oil, and inhibited shrinkage in convective drying and caused to change into porous structure after the drying. The inner structure of dried potato was observed by X-ray computed tomography, and it was confirmed that the porosity was increased from 25 to 57 % for samples softened by impregnation of macerating enzymes. Analysis of the mechanical properties of dried potato using an instrumental measurement suggested that the impregnated emulsifier miniaturized the void shapes and that the impregnated oil changed the sample’s brittleness. It was found that the use of a 10-15 % (w/w) oil concentration in the impregnating solution was suitable for producing a brittle structure. This study showed that the freeze-thaw impregnation technique contributes to the quality of dried foodstuffs.
To establish a method of enzymatic peeling in the melting type of white flesh peach, we examined enzyme type and concentration, the effect of surfactant addition, and temperature in the promotion of enzymatic peeling. Acremocellulase KM can be applied to enzymatic peeling in the melting type of white flesh peach with a 2-3 h incubation. Promotion of enzymatic peeling by surfactant addition was confirmed for three enzymes, although the effect was small with Acremocellulase KM. At room temperature (32.4±1.0 °C), enzymatic peeling required a 2-3 h incubation with a 0.25 % solution of Acremocellulase KM. Acremocellulase KM treatment time was shorter under higher temperatures; however, fruit injuries were observed at 5 °C, 40 °C, and 50 °C. Therefore, room temperature is considered more appropriate (26-30 °C) for Acremocellulase KM incubation. Thus, Acremocellulase KM is suitable for enzymatic peeling in the melting type of white flesh peach, conducted with a 2-3 h incubation using a 0.25 % or greater enzymatic concentration at room temperature (26-30 °C).