Recently, the environmental impact of large amounts of waste and by-products generated from agricultural products has become a serious issue. Food waste, in particular, presents not only environmental challenges but also economic concerns. As part of the Sustainable Development Goals (SDGs), a target has been set to halve per capita global food waste by 2030. In this context, ongoing research aimed at the effective utilization of unused plant resources, including food waste, non-edible parts of agricultural products, and by-products, has been carried out. For over 20 years, the author has conducted various studies, primarily from an analytical chemistry perspective, focusing on unused food resources often discarded or underutilized. The research has specifically targeted unused plants, analyzing their components (including polyphenols) and evaluating their functional properties to provide scientific evidence for their biological activities. This article highlights some of these research findings. In particular, the studies have focused on unused agricultural products such as wasabi leaves, fruit peel of akebi, anthocyanin-rich food materials like berries, and bee products such as propolis and bee pollen.

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.

When surimi containing nitro blue tetrazolium was heated with vitamin C (AsA), the color intensified. This coloration faded upon the addition of tiron, a scavenger of the superoxide anion radical (), indicating that was generated from AsA in the surimi. In myosin prepared from carp, the generation of thiyl radicals (S•) by was detected using electron spin resonance spectroscopy. These results illustrate the quality improvement mechanism of AsA in gelatinous protein foods as follows: (1) AsA added to surimi reduces the transition metal, which becomes oxidized, (2) O₂ is reduced to via one-electron reduction, (3) pulls hydrogen radicals (H•) from the SH group on myosin to form S•, and (4) disulfide (SS) bonds are formed between myosins by radical oxidation, which leads to a denser structure and a quality improvement effect. When cream chicken was prepared using the vacuum cooking method, separation was observed in the sauce. This phenomenon was caused by the dissolution of soluble proteins in the meat during heating. The soluble protein was examined by scanning electron microscopy and was found to consist of spherical particles in a random structure at 75°C heating; upon heating to 90°C, the SS bonds formed a strong structure, resulting in a more uniform material and forming a gel with a wide space and a large surface area. Thus, heating to 90°C is speculated to be the reason for the separation of the source, as the structure at 90°C firmly held the casein micelles and oil droplets. In the functional alteration of chicken myofibrillar proteins (Mfs) through glycation, using the Maillard reaction, the solubility of protein in low-ionic-strength solutions and the antioxidant capacity were determined. The glucose-modified chicken Mfs showed antioxidant capacity in the heated gel. In contrast, the glucose-modified soybean 11S globulin showed high emulsification stability, indicating the possibility of developing an emulsifier that suppresses oil autoxidation. As an antioxidant, soybean 11S globulin was also found to be sufficient to suppress oil oxidation.

Anti-inflammatory and anti-allergic activities of dietary fiber (lentinan and fucoidan) are reviewed. We reported that lentinan, β-1,3; 1,6-glucan derived from Lentinula edodes, suppresses intestinal inflammation and ameliorates symptoms of colitis. Furthermore, as a mechanism, our study revealed that lentinan suppresses intestinal inflammation by Dectin-1-mediated regulation of tumor necrosis factor receptor 1 transfer to the surface of the intestinal epithelial cells. We revealed that fucoidan derived from Saccharina japonica inhibits mast cell degranulation through the upregulation of galectin-9 content in the blood. We found that residual amounts of IgE on RBL-2H3 cells were decreased by the addition of galectin-9. Galectin-9 was demonstrated to be capable of removing IgE even if IgE was already bound to mast cells and to suppress the mast cell degranulation induced by antigen. This study shows that lentinan and fucoidan might become effective therapeutic agents for patients who have already developed intestinal bowel diseases and type I allergic diseases, respectively.

Research and development of functional food materials and functional foods with the goal of "contributing to the maintenance and improvement of people’s health through food" were conducted. Phosphoryl oligosaccharides of calcium (POsCa), highly branched cyclic dextrin (HBCD), and α-glucosylhesperidin (Hsp-G) were synthesized using enzymes, and POsCa was utilized for caries prevention, HBCD increased endurance performance, and Hsp-G improved poor blood circulation, which could be put into practical use. Subsequently, based on the knowledge and experience gained from these studies, the research was expanded. In oral hygiene, we have developed biscuits for the elderly that are easy to chew and swallow, and tablets that suppress halitosis by removing tongue coating using protease. Research on glycemic control derived from endurance performance studies has led to the development of rice crackers for diabetics and the research on persimmon polyphenols found they suppress postprandial blood glucose. The knowledge of autonomic nerves gained in research on blood circulation led to the development of stress-reducing chocolate using GABA and the search for ornithine that promotes sleep. In addition, a study on the post-growth health of offspring born from undernourished mother based on the DOHaD theory found that cross-generational nutrition was very important.

Microengineering-based structuring and valorization of lipid foods were investigated. First, to control the fatty acid composition of triglycerides, modified lipases were prepared using emulsifiers and fatty acids, and applied to interesterification of fats and oils. Stearic acid was suitable for lipase activation, showing high interesterification activity. The structure of stearic acid-modified lipase was first analyzed by small-angle X-ray scattering. Next, the membrane separation performance for crude oil was investigated using hydrophobic non-porous membranes. Degumming and decolorization tests for crude soybean oil were conducted, revealing that the rejection of phospholipids and the decolorization ratio were more than 95%, representing higher quality compared to conventional methods. Membrane application to used edible oil also showed better performance than the conventional adsorption method. For practical use, improvement of the permeate flux is needed. Finally, a technology was developed for preparing monodisperse emulsions using fabricated microchannels (MCs). Efficient emulsification was achieved using asymmetrically structured MCs. The slit structure caused large distortion of the oil-water interface, and the interfacial tension induced spontaneous droplet formation. Laboratory-scale MC emulsification equipment was industrialized and used for various applications.

This review describes studies on ensuring the microbiological safety of food. These studies contribute to the processing and storage of high-quality and highly safe foods. The studies are focused on these areas of investigation: 1) simple and rapid methods for detecting and identifying various foodborne pathogens and bacterial toxins; 2) scientific evidence at the basis of hygiene management for the production of agricultural produce, such as food poisoning bacterial contamination from the cultivation environment of produce that are raw materials for food products and the survival of pathogens on the produce; 3) effective decontamination methods through the combination of treatment with detergents and sterilizers for agricultural produce; and 4) elucidating the mechanisms of action of food ingredients on growth inhibition of vegetative cells and spores, on activity of bacterial toxin, and on inhibition of biofilm formation of foodborne pathogens that are the basis for the development of safe storage technologies for food. The findings of these studies contribute to improving the microbiological safety of foods, which leads to the development of food science and technology and the food industry.

Food chemistry studies on enzymatic browning and the Maillard reaction were reviewed. Enzymatic browning can broadly be categorized into immediate and delayed types. We investigated the mechanisms and regulation of enzymatic browning of apple as an example of the immediate type, and browning of lettuce and mung bean sprout as the delayed type. The Maillard reaction is the major cause of non-enzymatic browning. However, melanoidins, which are the major brown pigments formed by the reaction, are large, heterogenous, high-molecular-weight compounds with chemical structures that are difficult to elucidate. We therefore focused on the low-molecular-weight pigments formed by the Maillard reaction. We identified various novel pigments in model systems and foods based on instrumental analyses.

Food emulsions are thermodynamically unstable systems due to destabilization processes such as flocculation, creaming and coalescence. Thus, the maintenance of kinetic stability is critically important to obtain high-quality commercial products. Our group has been studying the adsorption behavior and interaction at the interface of several components in oil-in-water emulsions, particularly, the two major components, i.e., proteins and low-molecular weight surfactants (emulsifiers) to understand the factors governing quality of food emulsions. In this review, I show the main results of our studies on food emulsions over the past 30 years. The topics are as follows: 1) the interaction of proteins and emulsifiers, particularly the displacement of proteins from the interface by emulsifiers; 2) Fat crystallization as a cause of partial coalescence of oil droplets; 3) Emulsion formation and stabilization by adsorption of fine particles; 4) Rapid evaluation of long-term stability of emulsions.

Our studies on food science and technology for development of high quality food were reviewed. A series of papers deals with food aroma: 1) off-flavor generation in Satsuma mandarin juice during a pasteurization and improper storage, 2) aroma evaluation of coffee and sesame seed oil by multivariate analyses of GC data and sensory data, 3) analytical study on off-flavor of skim milk powder, 4) preparation of odor concentrate by solid phase extraction, 5) non-enzymatic formation of lactones in butter oil, 6) improving the palatability of salt-reduced food using soy sauce aroma, 7) characterization of odor terminology in Japanese, and 8) aroma sorption into plastic materials. A series of papers deals with food process engineering: 1) microbial and enzymatic inactivation under high pressure carbonation, 2) microbial inactivation by the high pressure hydrostatic treatment, and 3) rapid hygrothermal pasteurization of fruits and vegetables using saturated water vapor.

The author has been conducting research into improving the sensory and processing properties as well as the health-promoting functions of foods, and evaluating the physiological functions of food components with agreeable sensory properties, with colleagues and students in my laboratory. Among the sensory and processing properties, expansive properties of protein-fortified breads and foaming, emulsifying and gelling properties of food proteins were improved. Among the health-promoting functions, improvement of nutritional value, inhibition of platelet aggregation, reduction in allergenicity, prevention of hepatic injury, suppression of hyperglycemia, and enhancement of calcium absorption were achieved.

We investigated the structural and functional properties of polysaccharides that constitute the cell walls of plant foods (including dietary fiber). We established methods to determine the fine structure and quantity of xyloglucans (XGs) and compared the structures of XGs from commonly consumed vegetables, fruits, and grains. The results demonstrated that XGs had different structures depending on the type, variety, and ripeness of the products. Glucuronoarabinoxylan (GAX) isolated from the primary cell walls of grasses contained ferulic acid esterified to its arabinose side-chains. Oligosaccharides originating from XGs and GAXs were found to have physiological functions. Water-insoluble cell walls (dietary fiber) had molecular sieving properties and delayed the diffusion rate of glucose in vitro.

Moreover, we explored potential added value of local agricultural, forestry, and fishery products, including unused resources, by analyzing their components, mainly polysaccharides. The following are the major findings of our research. (a) We developed a method to brew vinegar from apple pomace. This method involved treatment of the material with commercial bacterial enzymes to generate health-promoting oligosaccharides that remained in the final product, unutilized by yeast or acetic acid bacteria. (b) Using purple-black rice bran containing antioxidant anthocyanin pigments, we developed processed food that could serve as a rich source of health-promoting oligosaccharides, in addition to having high polyphenol (anthocyanin) and GABA contents. (c) We determined seasonal changes in the amounts of nutrients and health-promoting ingredients in Ecklonia stolonifera growing off the coast of Oma town, Aomori Prefecture. (d) We characterized the structure of proteoglycan (PG) present in salmon nasal cartilage. For the mass production of inexpensive PG-containing dietary ingredients, we established methods to defat (with water) and powder salmon nasal cartilage and to extract its PG fraction with hot water. We confirmed the safety of the resulting PG-containing product, demonstrated its skin anti-aging effects after oral administration, and developed a food item from the hot-water extract.