Americans invented, and once even embraced, those cardboard-like frozen TV dinners back in the 1950s, but today’s consumers won’t tolerate anything but the freshest tasting foods. Even if it’s not farm-to-table or made from scratch, the foods consumers buy need to have a top quality look and taste that could rival their favorite restaurants. Consumers determine freshness by judging a food’s appearance, texture and mouthfeel, as well as flavor and aroma.
But as much as consumers value freshness, they also value time, making convenience foods more critical than ever to a high-paced environment. People don’t want to wait long for entrées to hit the table, even in high-end restaurants, much less when they are hungry and tired after a long day and a stressful commute. The constant challenge for food makers, however, is to marry the seemingly conflicting demands of just-made freshness with long shelflife convenience and speed of preparation.
Nowhere do all the disparate needs seem farther apart than with a product that symbolizes fresh prepared foods better than any other: sushi. It’s the one product very few Americans make at home, but it takes time, either when going to a restaurant to have a sit-down sushi dinner or even to wait for it to be made to go. Most sushi restaurants and sushi retailers such as supermarkets that prepare it in the early part of the day to serve the lunch and after-work grab-and-go crowd, find keeping the packaged version of the products fresh and tasty is a huge hurdle.
In addition to the absolute freshness of the fish, sushi actually is about the rice more than what it is wrapped around. All sushi—with or without raw fish—is built around the sweetened rice vinegar-flavored steamed rice.
Some sushi makers prepare their sushi rice in advance and others looking for the ultimate convenience even freeze it. This runs the risk of starting starch retrogradation. Even refrigerated rice will begin to suffer staleness and breakdown of its texture within a short period of time.
Presented with the task to create a sushi product that could survive a longer shelflife, an option presented itself that took advantage of the unique characteristics of a multi-functional disaccharide called Trehalose. Trehalose is naturally found in many common foods such as mushrooms, baker’s yeast, and even honey.
It turns out that the addition of a small amount of trehalose was able to delay staling in sushi-grade rice and off-flavor development in overall sushi. That protection from this sort of degrading in taste and quality can be mitigated with the incorporation of trehalose. This made it possible for chefs and other product makers using delicate aromatic rice in formulation to deliver fresh-tasting products, with maintained and appealing mouthfeel and moisture, even if prepared well ahead of time and frozen.
By adding trehalose to the rice/water mixture at 2-5% by rice weight before cooking, trehalose helps ensure that the rice remains of good quality after it is refrigerated or frozen and thawed. The trehalose also helps maintain the rice’s stickiness, suppresses any hardening of its texture and, best of all, reduces flavor off-notes caused by storage. It even maintained the rice’s glossy appearance.
The trehalose should be completely solubilized before cooking the rice. For the best results, an additional 5% water was added to the formulation and this is recommended across the board when using trehalose because of the solubilization need. Without the extra water, the sushi rice will have a harder texture than sushi rice made without trehalose.
In the case of sushi rice, which is traditionally made with sweetened rice vinegar, the trehalose ingredient performs best when added to both the rice/liquid mixture before cooking (at 2-5% by rice weight) as well as to the vinegar solution (at 10%) incorporated into the rice after it has been cooked. To make the rice, it first was soaked for 30 minutes to an hour in water, then drained. The rice was then combined with the trehalose plus some dashi and mirin to the rice cooker and cooked.
For the vinegar component, vinegar, salt, sugar, and trehalose were measured into a pan, then warmed over a low heat until the ingredients dissolved. The finished steamed rice was transferred to a wooden mixing bowl and sprinkled with the vinegar mixture and incorporated gently throughout with a spoon.
Trehalose`s advantages come from how its molecules are structured. A water molecule can fit easily between its two glucose molecules. That gives trehalose a high water holding capacity, Trehalose entraps water between the substance and itself, stabilizing the original structure. This stabilizing quality is highly desired in frozen applications.
When frozen in a solution, trehalose forms smaller crystals than solutions that don’t contain trehalose. So instead of a food product’s cellular structures becoming stressed or destroyed by the freezing process, less cell damage occurs with the inclusion of trehalose. This goes a long way toward overcoming the challenges of freeze-thaw damage.
In fact, trehalose showed positive benefits to traditionally frozen formulations. Its smaller frozen crystal size, combined with its low sweetness, made using it in sorbet a decided advantage. At 5-8% trehalose of the total weight of ingredients, it was able to improve scoopability and mouthfeel, resulting in a premium, flavorful, high-quality product while still allowing the fresh flavors of fruit to stand out.
Another example of using trehalose to add multiple benefits was in a dried fruit product. In this formulation, the trehalose allowed the natural fruit flavor to shine while helping the finished product retain its natural color and juicy texture over time. Trehalose maintained the freshness and quality—important drivers of consumer demand when it comes to the need for freshness maintenance in prepared foods.
Trehalose is only mildly sweet (although it still provides 4kcals/g). It is easy to use in food applications because it allows the natural flavor to come through. This proved desirable when creating products, such as a prototype of a gluten-free cheese cracker. The addition of trehalose actually resulted in a stronger cheese flavor, which could allow a manufacturer to potentially reduce the total amount of added flavor used.
Trehalose’s flavor advantage also translates as an especially huge benefit for a commercial
reduced-sodium poultry product. When potassium chloride is used to reduce sodium in a chicken or turkey entrée, it can give the poultry product a bitter, metallic aftertaste. Surprisingly, trehalose can mute this aftertaste while still enhancing the product’s saltiness. This is because it provides a more balanced sensory profile, making it easier to produce a better tasting sodium-reduced product.
Balance also is key in glazed baked goods. Glazed donuts are a challenge for bakers because they must be consumed fairly immediately after production. This is because the glaze begins to draw moisture from the donut. In short order, this causes the donut to stale and the glaze to weep. By suppressing moisture migration, trehalose extends the shelf life of fresh donuts.
Texture is increasingly being used to confirm if a product is “real,” “fresh,” or less “processed.” Trehalose is able to give baked goods and snacks enhanced crunchiness, a lighter texture and longer shelf-life. It also improves the softness and juiciness of cooked proteins due to its ability to stabilize proteins.
This article based on an interview with Anne Ciputra, technical services manager for Cargill Corn Milling, North America. Across a 10-year career, she has gained international working experiences in the areas of product development, quality, regulatory, technical sales, and international trade and business development. Following obtaining her degree in food technology from the University of Pelita Harapan in Indonesia, Ciputra now has worked for a number of food industries in several different countries. She can be reached at www.cargill.com or through this magazine.