On the afternoon of August 21, Professor Noriyuki Tanaka, Professor Koichi Takaki, and Associate Professor YUAN Chunhong, from Iwate University in Japan delivered online lectures entitled “New Technology and its Application in the Fishery of Japan”. The event was host by professor HU Yaqin.

At first, Dr. Noriyuki Tanaka gave a lecture on “No Waste Usage of Fisheries Resources - Traditional Practices and Future Prospective”. He briefly introduced the trend of food security for global population. He pointed out that annual loss and waste along the food is ubiquitous, about 30% in cereal products, 40%-50% in fruits and vegetables, including roots and tubers. Besides, with increasing importance of marine food in the diet,  people call for effective usage and sustainability of marine products for ecological balance.

So why not eating whole which provides us perfect nutrition? Dr. Tanaka introduced the idea of whole food and its development. Japanese traditionally tried to use or eat everything they caught or collected from wild-life (In Japanese, Marugoto shoku 丸ごと食), because they think that any healthy animals’ composition is the same as theirs. In 2000s, whole food concept met “shokuiku食育”, then expanded as a movement to harmonize diet, health, life and environment. And there are more activities on whole food in Japan in recent years, such as book publication, seminar and cooking school, visiting farms, etc.

Then, Dr. Tanaka reviewed some processed sea-foods with merit and demerit analysis, including simmered fish in sweetened soy sauce, salted and fermented squid, tempura of small fish, primitive “SURIMI”, fish sauce and other typical course dishes in Kindaitei restaurant. Problems like too hard, too much salt, too much sugar, or too much fat in traditional way need to be solved. These must be adapted to meet both younger generation and elderly’s needs. Therefore, it is of great significance to develop science-based approaches rather than trial and error with experience-based methods.

Finally, Dr. Tanaka ended the lecture with the sentence “You are what you eat!”. He encouraged students to seek for further advances to protect marine ecosystems, and to maintain sustainable sea food utilization to meet future food demands.

Next, Dr. Koichi Takaki gave a lecture on “Pulsed Power and Plasma Applications for Agriculture and Food processing”. He introduced his research on development and employment of repetitively operated compact pulsed power generators with a moderate peak power for applications of agriculture and food processing.

Electric power is a kind of new technology, which could easily change to heat, stress, radicals, etc. When electric field exceeds breakdown electric field (35.5 kV/cm for air), electrostatic discharge (plasma) occurs. Plasma is widely applied in surface functionalization, protective coatings, semiconductor industry, biomedical, packaging, energy production, nano-science, etc. For agricultural applications, plasma can be used for productivity improvement, and infection inhibition of plants before harvesting; fresh-keeping of products, losses avoidance in preservation and transportation of fruits and vegetables after harvesting; valuable components extraction and additional value during food processing.

Then, Dr. Takaki explained the possible mechanism of plasma. For example, pulsed electric field (PEF) has impact on protein 3D structure change, which affects the enzyme activities. Besides, pulsed high-voltage produces intense high-electric field which can cause some biological effects such as stress response (stimulation) and electroporation. Types of pulsed power also have biological effects, including reactive species such as ROS and RNS, which are caused by gas and water discharges. These active species (·OH and ·O₂^-) contributes to inactivation of bacteria, reducing the infection risk.

Dr. Takaki  has made a lot of advances in the plasma  technology application. The pulse discharge is used for promoting growth of the vegetables and fruits. The growth rate of the vegetables and sugar content in the harvested strawberry increased by the plasma irradiation to the hydroponic solution. The pathogenic bacteria R. solanacearum in the liquid fertilizer decreased from 10⁷ to 10² CFU/mL by the plasma treatment.

The pulse high-voltage improved the mushroom yield. The yielding rate of Shiitake mushroom (L. edodes) is increased with the high-voltage stimulation in fruit-body formation phase, not only in size, but also in mushroom multiply. And the good news is that mushroom cultivated using this technology has already on sale now.

The AC high-voltage keeped freshness for a relatively longer period of agricultural products. The electrostatic effects suppressed the permeation of small protein, which contributed to removing airborne bacteria and fungi spore from the storage house and container. This removal decreased the infection risk with fungi and bacteria.

The pulse DBD remediated air and liquid to inhibit degradation of agricultural products via ethylene removal through oxidization reaction. Some kinds of fruit and vegetable emitted the ethylene gas which accelerated the degradation of other kinds of fruits and vegetables.

These applications provide a potential food supply chain in the world. Currently, this technique is used for agricultural products. Maybe applications in marine food can be further explored in the future.

At last, Dr. Chunhong Yuan gave a lecture on “Recent Freshness Preservation Technology of Fish and Shellfish from Catch to Consumption in Japan”. She mainly introduced “What is freshness”, “How to keep freshness”, and several case study in Japan on fishery products.

The consumption of fish and shellfish products has been increasing steadily in recent years due to the broad awareness of the health and nutritional benefits of seafood, as well as cultural influence and social status symbol. Sashimi (Sliced raw fish meat) and Sushi, originating from Japanese cuisine has gained popularity worldwide, and become one of the fastest growing food segments in food industry today. The most popular sashimi or the topping of sushi mainly include but is not limited to shrimp, squid, salmon, tuna and other marine fish or co-products. The fish used as a raw material must be fresh.

Dr. Yuan presented recent scientific viewpoints of new techniques and technologies for freshness preservation and safety assurance of fish and shellfish in Japan, especially the case study of spotted mackerel (Scomber australasicus) and Japanese scallop (Patinopecten yessoensis). Postmortem change of fish develops from pre-rigor, rigor, post-rigor, and decay. The fish freshness is highly correlated with indexes of pH, ATP, K value, microstructure, texture, myofibril ATPase, sensory evaluation, TVB-N, TMA, TBARS, TPC, etc. Among them, K value is the key index to evaluate the freshness of aquatic products.

Fish freshness maintenance involved key technologies to develop high quality, freshness-keeping technology, including catching, killing and storage, as well as freezing and thawing to avoid drip loss. pH and ATPase activity decreased quickly after fish death. Different killing methods showed large effects on initial post mortem period. Besides, instant freezing kept high quality, possible for value-adding. Application of slurry ice (small, spherical crystals) decreased the damage to fishery products and prolonged its shelf-life. Moreover, FDA guidelines demonstrate that freezing treatments are required to kill parasites for consumer safety reasons. And it is illegal to serve raw fish (sashimi) that has not been previously frozen.

According to Dr. Yuan’s research: 1. Keeping scallop in shell during cold storage might be useful for keeping scallop freshness and quality during market distribution; 2. The ATP-related compounds decomposition rate of the scallops after frozen-thawing increased significantly during storage; 3. K-value for freshness evaluation differed between fresh and frozen type; 4. AdR is difficult to be detected during storage in scallop; 5. There is a  small amount of IMP accumulation in scallops, and the decomposition rate of IMP is very low during storage.

Three professors from Iwate University delivered a special lecture of new technology developments in fishery products. They also demonstrated potential research interests and further challenges of current technology. Students were encouraged to explore further research and application in this field.