“You are wasting taxpayers’ money!” His mother’s harsh words motivated him to extensively explore ways to determine the maturity of fruits without cutting them.
Professor Sakurai specializes in plant physiology, a discipline that studies the growth and development of plants. His most noted research concerns the “development of nondestructive methods of measuring fruit quality.”
   Several methods of checking the ripeness of fruits have been introduced so far. Initially, these methods assessed only sugar content through image analysis or near-infrared spectroscopy. These conventional means, however, were limited in that they were not applicable to varieties that do not let light through and that they were incapable of sorting out overripe fruits. Meanwhile, it has been known since olden times that firmness is one of the reliable criteria for determining whether a fruit is ripe for the picking. In fact, it has long been a routine practice for fruit farmers to put a stick into the flesh of fruits to check their ripeness. Besides, according to Professor Sakurai, Japan is the most meticulous of all fruit producing countries in terms of fruit quality assessment
   “That is a reflection of Japanese consumers’ enthusiasm about eating delicious foods,” says the professor. And that is why there has been a need in this country for even more effective means of fruit quality assessment.
About 20 years ago, Professor Sakurai went to the U.S. to conduct research on tomatoes and learn various relevant techniques for a period of one year. His destination was UC Davis in California. The university conducted numerous studies on tomatoes because the UC Davis campus was located in the middle of a major tomato producing area that represented a quarter of the volume of tomatoes processed worldwide.
   While in the U.S., Professor Sakurai was asked to physically assess the maturity of tomatoes. So he cut tomatoes, stuck a needle into their flesh, measured the resistance that was generated, and organized numerical data obtained to produce a scientific paper. On his return home, he exultantly told his mother about his accomplishment in the U.S. However, his mother sniffed at his story, saying, “I’ve already known about your ‘findings’ because I cut tomatoes every day. It is a sheer waste of taxpayer’s money to put into those difficult figures what you can clearly see just by cutting tomatoes!”
   Determined to impress his mother next time around, Professor Sakurai embarked on a new research project.

 An encounter that resulted in the development of a “nondestructive” technique for assessing the ripeness of fruits from their firmness
Guided by the intuition that the “sound” may be the key parameter, Professor Sakurai started an experiment in which the sound of various frequencies was applied to fruits so the fruits could “hear” it and the sound waves that passed through the fruits were received with a microphone.
   Based on his findings, Professor Sakurai wrote several papers, but he was somewhat uncomfortable about continuing that research project. At the time he almost decided to end the project, he was spoken to by a person from a certain company during an academic society’s poster session.
   When that person asked “What are you interested in doing?”, Professor Sakurai explained about his research interest. The person responded, “Maybe we can help you. I will send you documents after I get back to my company.”
   After a few days, Professor Sakurai received a bundle of documents several centimeters thick. Some documents suggested that it might be the vibration rather than the sound that is the key. A brochure concerning vibration measuring devices was also attached. This was the professor’s first encounter with the laser Doppler vibrometer.
When given a vibration, any object resonates with a unique resonance frequency. Using this rule, one can determine firmness and maturity of fruit. Because the formula necessary for the procedure had already been developed by a physicist many years ago, all one had to do was apply the obtained data to the formula. Convinced of its potential, Professor Sakurai embarked on studies of this technique somewhere around 1994. For nearly 20 years since then, he has been engaged in research on this method.
   “This vibration technique is a good means of collecting internal information from living things,” says the plant physiologist. Although vibration technology itself is advancing day by day, its application to fruit is unprecedented and Professor Sakurai is the world’s first scholar to refine fruit quality assessment procedures using vibration technique to this extent.
   In 2005, based on his research results, Professor Sakurai founded Applied Vibro-Acoustics Inc. (AVA) in Hiroshima University’s Venture Business Laboratory. In the ensuing year, in cooperation with a professor who is also his senior researcher, the plant physiologist established Yamamoto Kagaku Kogyo Inc., a company engaged in the development of a small device that has the same level of precision as the laser Doppler vibrometer.
Aspiration to see the laser Doppler vibration promote Japanese agriculture and lead to the establishment of “Japan Brand”

Asked about the joy of his research, Professor Sakurai says, “The most exciting part of it is to hear from someone about specific ways in which the techniques I developed are helping him or her. It is indeed a pleasant surprise to find that these techniques are being used for various unpredictable purposes. I really enjoy working in my lab every day, measuring many different things.”
   Furthermore, the professor continues, “One of these days, we will have kiwifruits, avocados, and a number of other fruits on supermarket shelves with ‘Best Period to Eat’ labels, showing shoppers specific dates on which these fruits become most delicious. Also, fruits such as watermelons sorted and bred using my vibration technique may be distributed in the market someday, though such application is invisible. In the years to come, I would like to work on the La France pear and other fruits whose smells and colors do not help at all in determining their maturity.” Given the professor’s strong commitment to his research, we may have a chance to see the “fruits” of his endeavors with our own eyes in the not-too-distant future.
   Professor Sakurai’s methods will also help establish “Japan Brand” and promote agricultural exports. “If we can determine when a fruit will be at its best, we will be able to reduce losses and increase consumption, thereby rewarding producers for their efforts. It is my hope to build that kind of mechanism and contribute to ‘aggressive farming.’”
Naoki Sakurai
Evaluation of Plant Environment Laboratory
Hiroshima University Graduate School of Biosphere Science
August 1, 1980 – September 30, 1988: Research Associate, Faculty of Integrated Arts and Sciences, Hiroshima University
October 1, 1988 – March 31, 1993: Associate Professor, Faculty of Integrated Arts and Sciences, Hiroshima University
April 1, 1993 – March 31, 2006: Professor, Faculty of Integrated Arts and Sciences, Hiroshima University
April 1, 2006 – Present: Professor, Hiroshima University Graduate School of Biosphere Science

Retired on March, 2016