Course:FNH200/Projects/2024/Sushi

Introduction

Sushi & Sashimi Platter

Sushi (すし, 寿司, and less commonly 鮨) is a diverse Japanese dish that revolves around differing presentations of sushi rice (しゃり, shari). The dish generally consists of vinegared rice prepared with a type of seafood, however large variety of ingredients are also commonly used like various meats, vegetables, and sometimes tropical fruits. Hanaya Yohei is generally credited as the inventor of modern sushi, which is regularly served with pickled ginger (ガリ, gari), wasabi (ワサビ, わさび, or 山葵), and soy sauce.

History

The evolution of sushi ingredients has been marked by both tradition and innovation. Historically, sushi primarily utilized raw fish and seafood, reflecting Japan's rich coastal resources. The earliest form of the dish dates back to the Yayoi period (circa 300 BC to 300 AD), today referred to as narezushi (馴れ寿司, or "matured fish"). During the earliest iterations of sushi, the fish was fermented with vinegar, salt and rice, after which the rice was discarded. The dish evolved when people began to eat the rice as well as the fish during the Muromachi period, from 1336 to 1573. It was then during the Edo period (1603 - 1867) did vinegar eventually replace fermented rice.

Tamagoyaki or tamago sushi

Over time, the introduction of alternative and sustainable ingredients has diversified the sushi landscape. One notable trend in ingredient innovation is the use of sustainable seafood options to mitigate overfishing and promote ecological balance. Modernly, some sushi restuarants have adopted practices such as sourcing seafood from fisheries that prioritize sustainability and the health of the ecosystems they are taking from.

Another approach to maintaining a healthy relationship with the environment is the increase in popularity of vegan/vegetarian sushi options. Hand-pressed sushi (nigirizushi) like the avocado nigiri, tamagoyaki (omelette) nigiri, and cucumber seaweed rolls (cucumber makisuzhi) are all very popular alternatives amongst vegetarians and non-vegetarians alike.

Ingredient innovations like these not only cater to contemporary tastes and ethical considerations but also preserve the essence of sushi as a versatile and dynamic culinary art form.

Storage Conditions

Specific growth rate (μ) in sushi as a function of storage temperature for total aerobic plate count

To ensure the safety and quality of sushi, it must be stored under specific conditions.

After receiving potentially hazardous foods like sushi, they should be refrigerated right away at 5°C (41°F) or lower. When making acidified rice for sushi, the rice should first be cooked and then cooled quickly to 5°C (41°F) before adding the acid. Acidifying the rice to a pH below 4.6 is essential to stop bacterial growth, and it’s important to check the pH to make sure it's done right. Acidified rice can be stored for up to 8 hours, but any leftover rice should be thrown out at the end of the day. If the rice isn't acidified, it needs to be kept in the fridge at or below 5°C (41°F) at all times . For both raw and cooked sushi, it’s crucial to wrap and refrigerate it properly to minimize exposure to air and moisture, which can cause spoilage .

Keeping the right temperature and maintaining cleanliness during preparation and storage is key to ensuring the microbiological quality of sushi and preventing foodborne illnesses. Moreover, raw fish and seafood used in sushi should be of high quality, ideally sushi-grade, and stored at -20°C (-4°F) or below for at least 7 days, or at -35°C (-31°F) or below for 15 hours to get rid of parasites. Frozen fish should be thawed in the refrigerator or under cold running water, never at room temperature. It’s also important to use clean utensils and cutting boards during preparation and to wash hands thoroughly to avoid cross-contamination .

Storage Technology

As the global popularity of ready-to-eat sushi meals increases, ensuring microbiological safety and maintaining freshness become critical challenges. Innovative technologies play a vital role in addressing these issues, extending the shelf life of sushi products while preserving their quality.

Techniques such as modified atmosphere packaging (MAP) and high-pressure processing (HPP) are being explored to inhibit bacterial growth and prevent spoilage. Advancements in refrigeration and cold chain logistics contribute significantly to maintaining the optimal temperature for sushi storage and transport.

Modified Atmosphere Packaging (MAP) Process

Modified Atmosphere Packaging

Modified Atmosphere Packaging (MAP) has shown promise in extending the shelf life of sushi. Extensive studies have demonstrated that diverse MAP compositions effectively inhibit microbial proliferation in sushi products by successfully suppressing the growth of both Total Aerobic Bacteria Count (TABC) and psychrotrophic bacteria in stored sushi. For instance, Chen et al. found that a mixture of 30% CO₂, 65% N₂, and 5% O₂ effectively reduced total aerobic bacterial counts in sushi stored at 25°C. Moreover, research conducted by Mol, Ucok Alakavuk, and Ulusoy examined the effects of two MAP conditions (50% CO₂/50% N₂ and 100% CO₂) on salmon hosomaki stored for 6 days at 4°C. They found that the 100% CO₂ atmosphere not only impeded microbial growth but also helped maintain the sushi's color parameters during storage. Overall, MAP techniques offer a practical and effective solution for maintaining the microbiological quality of sushi during storage.

Ultraviolet treatment

Ultraviolet (UV) radiation, particularly UV-C (200-280 nm), has emerged as an effective method for preserving sushi quality during storage. A study by Steffen, Duerst, and Rice demonstrated that a combination of UV-C with modified atmosphere packaging, ozone, electrolyzed water, and ultrasound could prolong the shelf life of ready-to-eat sushi to more than 7 days. More advanced UV technologies, such as Pulsed UV (PUV), have also shown efficacy in reducing microbial loads on raw fish and seafood components commonly used in sushi preparation.

Diagrammatic representation of cold plasma application in food matrices

Cold Plasma

Cold plasma provides a non-thermal decontamination technique for sushi preservation. Its key advantage is the ability to treat food without increasing product temperature, making it suitable for delicate sushi components. Studies have shown that cold plasma can reduce microbial counts in hosomaki (巻き寿司) samples (a type of makizushi (巻き寿司), or rolled sushi), where it extended shelf life by up to 4 days at 4°C. The versatility of cold plasma technology in its integration with other preservation methods like modified atmosphere packaging, makes it a promising avenue for enhancing sushi storage and safety.

Canadian Sushi Regulations

Sourcing of Ingredients

Sourcing of ingredients for sushi must adhere to strict standards. Seafood, particularly fish intended for raw consumption, must come from approved and reputable suppliers. These suppliers are required to provide documentation confirming that the fish has been frozen to eliminate parasites. The regulations specify that fish must be frozen at -20°C (-4°F) for at least 7 days or at -35°C (-31°F) until solid and stored at that temperature for 15 hours. Only sushi-grade fish meeting these criteria can be used for raw sushi preparations. Sushi rice must have a pH value of 4.2 or less to inhibit bacterial growth.

Preparation and Handling

The preparation and handling of sushi involve rigorous hygiene practices to prevent contamination. Food handlers must not engage in any other food preparation or business activities. Food handlers must wash their hands thoroughly and frequently. All surfaces and utensils used in sushi preparation must be regularly sanitized. Bamboo mats used in rolling sushi should be covered with cling wrap, which must be changed every two hours and sanitized daily. Additionally, measures must be in place to prevent cross-contamination. Separate cutting boards, knives, and utensils are required for raw fish and other ingredients. Raw foods, such as uncooked chicken and meat, must be stored separately and below ready-to-eat foods to avoid contamination from dripping juices.

Storage and Temperature Control

Proper storage of sushi ingredients is crucial to maintaining food safety. Fish and seafood must be stored at temperatures below 5°C (41°F). Prepared sushi should be kept refrigerated at 5°C (41°F) or less during transport, storage, and display. Sushi must not be left unrefrigerated, and any remaining rice at the end of the day must be discarded to prevent the growth of pathogenic bacteria.

Inspections and Compliance

Food handling establishments that prepare and sell sushi must obtain a permit to operate under The Public Health Act regulations. Regular inspections by Public Health Inspectors ensure compliance with food safety guidelines. These inspections focus on hygiene practices, storage conditions, and the proper sourcing of ingredients. Establishments found to be non-compliant with these regulations may face penalties, including fines, temporary closure, or mandatory corrective actions.

Exam Question Pitch

Q. Which of the following best explains why acidification and proper refrigeration are crucial for preventing spoilage organisms and pathogenic bacteria in perishable foods like sushi?

a. Acidification increases the food's acidity, which promotes the growth of beneficial bacteria, while refrigeration slows down the natural enzymatic breakdown of food.

b. Acidification lowers the pH to inhibit the growth of spoilage organisms and pathogenic bacteria, and refrigeration maintains a low temperature to further suppress bacterial growth.

c. Acidification makes the food more appealing to consumers, and refrigeration enhances the food's flavor profile by slowing oxidation.

d. Acidification reduces moisture content, which increases the likelihood of bacterial contamination, while refrigeration speeds up the growth of spoilage organisms.

Correct Answer:

b: Acidification lowers the pH to inhibit the growth of spoilage organisms and pathogenic bacteria, and refrigeration maintains a low temperature to further suppress bacterial growth.

Explanation for Exam Inclusion:

This question tests students' understanding of the dual role of acidification and refrigeration in food safety. Throughout the course, we learnt how acidification lowers the pH to inhibit the growth of spoilage organisms and pathogens, while refrigeration maintains a low temperature to further control bacterial growth. By integrating these concepts, the question reinforces the importance of both practices in ensuring the safety and quality of perishable foods, reflecting key learning outcomes related to food safety and spoilage control.