Investigation for mechanism of formation and strategy for reduction of the unpleasant taste derived from organic materials used in beverage vending machines 飲料販売機器で使用する有機材料に由来する異臭味の発生原理と改善方法に関する研究
Investigation for mechanism of formation and strategy for reduction of the unpleasant taste derived from organic materials used in beverage vending machines
In the present study, the mechanism of formation of malodorous compounds in two kinds of organic materials (synthetic hard resin containing antioxidants and silicone rubber cured with organic peroxides), as well as strategies to solve this problem, were investigated in order to improve the taste of beverages prepared by vending machines. The analyzed materials are thought to have significant effects on beverage taste, based on the author’s experience in the development and quality assurance of industrial beverage vending machines. For the particular case of silicone rubber, a production method was developed to achieve a balance of physical properties and taste inertness. Establishment of a Method for Taste Evaluation To characterize the unpleasant taste in beverages, an evaluation method was established by choosing appropriate indication/identification sensory evaluation tests. As a result, taste intensity was quantified by a combination of taste intensity rating with the three-cup alternative forced choice method. At the same time, a method to measure the detection threshold was established by using the best-estimate threshold (BET), in combination with the three-cup alternative forced choice method. When taste intensity was around 1-2.5 above the detection threshold, relatively high measurement precision was achieved. In addition, the detection thresholds of phenols evaluated by this method were consistent with reported values. Thereby, the taste intensity method was determined to be appropriate for the reliable evaluation of taste intensity in multiple beverages. Moreover, the best-estimate threshold method was determined to be appropriate for the evaluation of the detection thresholds of unpleasant-tasting substances. Influence of Hindered Phenols from Antioxidants on Beverage Taste in the Presence of Free Chlorine The taste of hindered phenols, which are commonly used as antioxidants for olefin polymers of beverage vending machines, was investigated to identify the cause of increased unpleasant taste in beverages after the addition of free chlorine to the source water. As a result, it was observed that more numbers of free (not substituted) 2,4,6 positions on the aromatic rings of phenols resulted in increased unpleasant taste when free chlorine was present. This suggests that the degradation of phenolic antioxidants, which generates less substituted phenols in the synthesized hard resin material, results in a debasement of the quality of the taste of beverages coming into contact with such material. Mechanism of Formation of Unpleasant Taste in Linear Low Density Polyethylene Containing Antioxidants by Heating during Injection Molding The influence of antioxidants added to linear low density polyethylene (LLDPE) on beverage taste was examined. The taste of water being in contact with molded PE changed depending on the kind of antioxidant used and on the presence of free chlorine. From the thermogravimetry/differential thermal analysis (TG/DTA) and pyrolysis gas chromatography/mass spectrometry (Py-GC/MS) results, it was determined that antioxidants experience degradation by heating during the molding process. In addition, some of the compounds identified by Py-GC/MS were also detected in the soaked water of the molded PE containing antioxidants. These compounds included mono- and di- substituted hindered phenols, which were proved to increase unpleasant taste in the presence of free chlorine. Therefore, the degradation of antioxidants caused by the thermal history during the molding process and its influence on beverage taste were demonstrated. Effects of Silicone Rubbers Produced by Compression Molding and Cured with Various Organic Peroxides on Beverage Taste, and Improvement by Post-Processing Treatments Compression molding silicone rubbers cured with various organic peroxides were investigated to evaluate and to prevent their negative influence on beverage taste. As a result, the manufacturing methods including two post-processing treatments were developed for each curing agent to reduce their negative effects on beverage taste, while at the same time, and to maintain the physical properties of the rubbers. As a result, some causative compounds of the unpleasant taste were identified. Acetophenone was found to be a major and common cause of the unpleasant taste. In addition, benzyl benzoate, which is formed by a reaction between vulcanization by-products, was shown to contribute to the unpleasant taste of beverages through the present study for the first time. The results of the present study can be applied to the hazard analysis (HA) of the unpleasant taste caused by the two kinds of organic materials used in beverage vending machines. Furthermore, the results of the present study can also contribute to decision of the critical control point (CCP) and quality control by HACCP, to assure and improve the quality of beverages dispensed by vending machines. It is expected that the application of the methodology presented in this study to all kinds of organic materials used in beverage vending machines will result in the development of a robust system to predict the contribution of each material to beverage taste.