Subtropical agricultural products are known to have distinctive flavor characteristics and various bioactive components, which can be attributed to their growth in harsh environments with intense ultraviolet radiation and high temperatures. However, comprehensive evaluation of the flavor characteristics and bioactive components of their processed products in combination with research investigating the functional enhancement of these foods is limited. This work addresses the improvement of palatability desired by regional agriculture and food industries, exploration of new food applications, and functional enhancement of the foods. Taking advantage of the Okinawan geographical location, the only subtropical region in Japan, we conducted studies on the flavor characteristics and bioactive components of subtropical agricultural products, including sugarcane, fruits, vegetables, and spices, along with their processed products and functionally enhanced products. In this paper, we primarily introduce the research findings focused on non-centrifugal cane sugar, shiikuwasha (Citrus depressa), sponge gourd (Luffa cylindrica), and their processed products.

Various types of rice flour are available in Japan, but the quality is inconsistent. Therefore, in order to produce high-quality rice flour consistently, it is necessary to establish guidelines for rice flour production. The author has identified the characteristics of rice flour that are conducive to making high-quality bread, sponge cake, and noodles. There guidelines indicate four indices: particles size under 75 μm, degree of damaged starch, amylose content, and water content. Among these, particles size under 75 μm, degree of damaged starch, and water content are recommended as common indicators across all applications when manufacturing products. The amylose content can vary based on the specific application of the rice flour. Aiming to produce rice flour that meets specific criteria, our institute analyzed rice flour samples from millers in Niigata Prefecture and provided feedback on the results. As a result, flour milling companies in Niigata Prefecture are able to supply rice flour with stable quality.

Three wild yeasts isolated at Kagoshima Prefectural College were identified through ITS4/ITS5 sequencing and characterized for their potential application to fermented foods and beverages. Carbohydrate utilization tests and fermentation experiments in dough were conducted for the isolated yeasts. Specifically, Lachancea fermentati (Lf-KPC1) underwent an additional fermentation test in high-sugar broth and bread evaluation. Lf-KPC1 demonstrated remarkable performance, fermenting equivalently or faster than commercial yeasts in three types of dough with various sugar contents, while the others exhibited low fermentation rates in high-sugar dough. Notably, the three wild yeasts exhibited higher freezing tolerance in dough. In high-sugar broth, Lf-KPC1 exhibited a unique capacity for simultaneous lactic acid and alcohol fermentation, suggesting its potential application in producing sour and low-alcohol beverages. The Lf-KPC1 bread contained more sugar and was more moist. This study concluded that Lf-KPC1 has promising fermentative characteristics, making it highly valuable for fermented products.

The primary objective of this study was to investigate the correlations between instrument measurements and sensory attributes of thickened liquids. For this purpose, a series of thickened liquids was prepared using different thickening agent contents from different sources, which were evaluated by sensory analysis for sensory attributes and by instrument measurements for specific physical properties. The texture attributes (hardness, ease of swallowing, and coating (oral cavity, residual feeling in the throat)) of 12 thickened liquid samples were investigated by sensory evaluation. The investigators were 10 panelists trained in evaluating sensory attributes. The line spread test (LST) and the short back extrusion (SBE) method were used for the instrumental analysis. The correlation coefficient between physical properties and each sensory evaluation value was also determined. The results showed that the apparent viscosity from viscosity measurements was highly correlated with each sensory attribute. As thickened liquid is a non-Newtonian fluid, the apparent viscosity was dependent on the shear rate. Hence, the instrumental texture perception of sol (thickened liquid) based on the oral cavity condition could be used to predict human texture perception based on the shear rate, which was obtained from the apparent viscosity similar to gel (strawberry jam). These results indicate that the SBE method is better than the LST for measuring the texture attributes of thickened liquids.

At the Small Research-Discussion on Cereal Grains in the annual meeting of the Japanese Society for Food Science and Technology in 2023, Dr. Tomoyuki Narisawa (Saitama Industrial Technology Center Northern Laboratory) gave a lecture entitled " What is the flavor of local flour in white salted noodle? :-Focusing on wheat from Saitama Prefecture-". They discovered a mechanism that lipoxygenase (LOX), an enzyme present in wheat flour dough, oxidizes unsaturated fatty acids to generate linear aldehydes (for examples: hexanol, heptenal, nonenal) and ketones, which express the unique flavor of local flour. In particular, it was confirmed that Norin 61 had significantly high LOX activity in the dough. Thus, the flavor of local flour in udon (white salted noodle) is thought to be caused by the oxidized odor resulting from the oxidation of unsaturated fatty acids caused by high LOX activity.

In this study, we investigated the factors involved in the flavor discrepancy between Norin61 and Satonosora wheat cultivars by analyzing the isozyme composition of lipoxygenase (LOX) and antioxidant levels. The results revealed that Norin61 exhibited a distinctive LOX isozyme composition, with a significant proportion of LOX-3, which correlates with its previously reported high LOX activity. Moreover, our analysis indicated that the content of lutein, an antioxidant present in flour, influences the formation of volatile flavor compounds. These results not only offer valuable insights for crafting products with specific flavors in the development of various wheat flour-based products, but also have potential genetic implications in the breeding of wheat cultivars boasting diverse flavors in the future.