Wednesday, November 6, 2013

Freshness Known

Anthony Bourdain is a well known chef and the Emmy award winning host of Parts Unknown, broadcast Sunday evenings on CNN. In this series he travels around the world offering a buffet of unique perspectives on the culture, geography, and cuisine of his various stops, the most recent being Tokyo. A story of Tokyo would be incomplete without an exposé on sushi, and for this he is lucky to know Naomichi Yasuda, his “mentor as far as all things related to sushi”, and his friend. “Over many epically delicious meals at his restaurant, he taught me everything I know about sushi. How to eat it. Where it comes from. Which is more important, the fish or the rice? Is fresher necessarily better? Everything.” For a great blog, clips and video on this episode visit http://www.cnn.com/video/shows/anthony-bourdain-parts-unknown/season-2/tokyo/index.html.

It is the last question to which his review piqued my interest - is fresher necessarily better when it comes to sushi?

I recently completed work validating the automation and detection of a new Freshness Assay developed by the French company NovoCIB for use in testing food muscle tissue. I used fish, including sushi, as validation samples. Abstracts of the work were accepted as podium presentations at both the Institute of Food Technologists (IFT) and International Association of Food Protection (IAFP) conferences held over the 2013 summer.

One of the most frequent questions I heard while doing this work was whether I was testing sushi. People seemed to automatically associate sushi with freshness. I even had one person specifically ask to test sushi or sashimi from a favored local sushi bar. I did (sashimi), and I compared it to sushi available at a grocery store chain in the area (both salmon). Here are some results:

sample graphs


These data show that sashimi from the sushi bar (right) produced an outlier, one piece has significantly lower levels of more than one nucleotide and higher levels of another (circled sample), whereas the grocery store sushi gave consistent index values over all 5 different samples. Context is important here for understanding any significance in these results to our enjoyment of the food itself, the safety of the food, or a decision about where to buy the ‘freshest’ sushi.

Inosine Monophosphate (IMP) is a by-product of the post-mortem ATP degradation pathway in muscle tissue (blue in the graph), and has been scientifically shown to be an important taste component in these foods. IMP further degrades to Inosine (Ino, green) and then Ino to Hypoxathine (Hx, red) over time. Hx is an indicator of tissue aging, and also tissue spoilage, but although higher levels of Hx may indicate that muscle tissue is older, or may have been thawed longer, it doesn’t always indicate that it is spoiled – or that it tastes bad. Quite the contrary, the complex flavor changes inherent from aging of food muscle tissue are closely guarded secrets that many great chefs and food manufacturers have developed a fine art in understanding. The freshness pathway taste timeline is different across species, and can also change due to storage time or other conditions (e.g. temperature). Chefs like Yasuda develop a unique talent for preparing exceptional sushi and sashimi based on their intimate experience and knowledge of this. As one example, Yasuda utilizes a ‘flash freeze’ technique to preserve meticulously selected tissue from world renowned Toyko fish markets at the height of good taste. In the United States fish served as sushi or sashimi must be previously frozen; however there are no standards regulating thaw conditions or quantified values of freshness. The lack of standardization is the most likely culprit in producing the outlier shown by the data, but I want to be careful to say that this doesn’t prove standards are necessary in sushi bars - diversity in presentation and taste, among other things (affordable prices) could be sacrificed if that were the case.

The scientific measure of taste and tissue aging has a useful place in an industry increasingly aware of both consumer safety and the need for a competitive edge in branding and cuisine presentation to appeal to the most buyers, though. The NovoCIB assay quantifies the peaks and valleys of freshness for any given condition in a muscle sample whether raw, frozen, canned, smoked, or pre-cooked in a microwave or other packaged meal or soup. This assay can help determine best buy dates, provide a consistent method for quality assurance testing, or as a research tool to study the effects of packaging and storage conditions on muscle freshness. Two new BioTek application notes are pending on this project, and a webinar co-hosted by NovoCIB founder and President Dr. Larissa Balakireva will be broadcast Q2 2014. Is fresher always better? Bourdain presents Chef Yasuda’s take on Parts Unknown (Season 2 Episode 7). Read the BioTek application notes and tune into the webinar to find out ours.

By: BioTek Instruments, Wendy Goodrich, Applications Scientist

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