The effect of transglutaminase enzyme addition on sensory and chemical properties of stirred yogurt

Dissertation for receiving a master's degree (M.S.c) in agricultural engineering

Food science and industry orientation

Yogurt is the most famous and widely consumed fermented milk product in the world. The most common defect in texture that leads to the non-acceptance of this product by the consumer is water loss. Nowadays, in Iran, condensed yogurt is mostly produced in the opposite way, that is, by adding dry matter to the stirred yogurt, they turn it into a thick and condensed state, and considering that these dry substances cause an unpleasant mouthfeel, therefore, adding a substitute such as transglutaminase enzyme can be important because it creates a network and increases viscosity, and also, compared to adding dry matter, it can create more favorable sensory properties. At the same time, adding transglutaminase reduces the cost of producing the product compared to adding dry matter. The aim of the current research is to produce blended yogurt with favorable quality characteristics using microbial transglutaminase enzyme for sale in the market. For this purpose, MPC (80 percent protein) at four levels (5.1, 2, 5.2, and 3 percent) and control (no MPC) and microbial transglutaminase enzyme at four levels (50, 100, 200, and 250 ppm) and control (no enzyme) were added to the milk and after undergoing the necessary operations to produce yogurt, physicochemical and sensory tests were performed, including measuring pH, acidity, viscosity, boiling, Consistency, flavor, color and general acceptance were performed on the samples during the first to twenty-first days of storage (at intervals of one week). The results showed that the control yogurt sample had the highest pH level on the first and last day of storage, and the lowest value belonged to the sample containing 200 ppm transglutaminar enzyme and 2% MPC. The trend of acidity changes during storage was increasing. The highest value was related to the sample containing 100 ppm enzyme on the last day of storage. A significant difference was observed between the samples with enzyme and control. With the increase in the storage time of the yogurt samples, the water content also increased. The highest amount at the end of the storage period was related to the control yogurt sample (without transglutaminase enzyme and MPC) and the lowest amount of watering belonged to the yogurt sample containing 50 ppm of the said enzyme.

In terms of aroma and taste, the yogurt sample containing 250 ppm transglutaminase enzyme and 51% MPC had the best score and the control sample had the lowest score. In terms of consistency, the yogurt sample containing 50 ppm transglutaminase enzyme and 3% MPC at the end of the storage period got the highest score. The color of the yogurt sample containing 250 ppm transglutaminase enzyme and 1.5% MPC had the highest score, while the consistency and color of the control sample had the lowest score. The highest overall acceptance score of the samples was related to all the samples except the control sample. The use of microbial transglutaminase enzyme has positive technological effects in yogurt formulation. The results of this research showed that it is better to add different percentages of this enzyme to yogurt to achieve the desired processing characteristics. Yogurt samples containing 250 ppm transglutaminase enzyme and 1.5% MPC have the highest color and flavor scores, and the yogurt sample containing 50 ppm transglutaminase enzyme and 3% MPC obtained the highest consistency score. rtl;"> 

Chapter One

General

1-1- Introduction

Yogurt is the most famous and widely consumed fermented milk product in The world is the result of the action of two special initiator bacteria, Lactobacillus delbruecki subspecies bulgaricus[1] and Streptococcus thermophilus[2]. Yogurt is a non-Newtonian fluid with a sensitive and complex structure (Serra et al, 2009, Sodini et al, 2005). The most common defect in tissue that leads to the non-acceptance of this product by the consumer is waterlogging.

(Fadela et al, 2009). In addition, hardness [3], viscosity (viscosity or stickiness) and creaminess are among the basic factors related to the texture of yogurt (Abbasi et al, 2007).

Watering phenomenon in yogurt directly depends on the amount of physical mixing, carelessness in the processing of milk such as very low pH and lack of temperature control during greenhouse storage, and it causes the network of protein micelles to collapse (Habibi Najafi, 1385., Gonzalez-Martinez et al, 2002). According to the definition of the International Federation of Milk and its Products (IDF) [4], fermented milks are products obtained from the fermentation of milk by the activity of specific microorganisms. These microorganisms must be alive, active and present in relatively large amounts when supplied and consumed. Meanwhile, after fermentation, phase separation should not be observed in the product (Khosrovidarani and Kushki., 2007 and Khurana & Kanawjia., 2007).

All types of yogurt are common in that the milk is fermented by Streptococcus thermophilus and Lactobacillus delbruecki subspecies bulgaricus, which grow synergistically in milk. Fermentation is done at 30-43°C for 2-5.2 hours. The choice of starter culture strains determines the fermentation time and the structure and taste of the final product (Mohabehi Tabatabai, 2012). Among all fermented milk products, yogurt is better known than other products and has more acceptance in the world. Yogurt is highly consumed in countries around the Mediterranean Sea, Asia and Central Europe. This product originates from Bulgaria and is called yaourt there (Karim, 1386).

Many countries have a special name for this product. The consistency and taste of yogurt varies from one region to another. In some places, they like its hard and high viscosity state, and in other places, its jelly and soft consistency. Yogurt is available in the markets of the world in a frozen form and as a dessert or in a watery form as a soft drink. The taste and flavor of yogurt is different from other acidified milk products, and its volatile and aromatic substances include a small amount of acetic acid and acetaldehyde (Farhnoudi, 1377).

Condensed or condensed yogurt is one of the common types of yogurt, which is known by titles such as Tan or Than in Armenia, Leben Zer in Egypt, Turba and Curut in Turkey. Today, for health reasons, cloth bags are used instead of animal skins for the production of condensed yogurt and are used in the nozzle separator industry. Some countries such as Lebanon and Jordan have made efforts to standardize this product, so that concentrated yogurt in Lebanon has a standard of certain chemical compounds based on fat, total solids, salt. Salt is basically added to the product as a flavoring or preservative agent or possibly to neutralize the acidic taste (Habibi Najafi et al., 1377).

In the last two decades, the desire to consume low-fat or fat-free dairy products, especially fat-free yogurt, has increased significantly due to the adverse effects of excess fat on human health. Consumers demand low-fat products with the same quality as high-fat products (Moidnia et al., 2011, Unal and Iski, 2003). Increasing the total amount of fat-free milk solids or adding natural or synthetic gums as stabilizers to milk are common and conventional methods used to improve the texture of low-fat yogurt. The required amounts of these additives to reach the same amount of solids as high-fat yogurt can cause unpleasant taste, excessive acid production during the storage period and create a sandy texture in yogurt (Ozer et al, 2007).

As we know, nowadays in Iran, condensed yogurt is mostly produced in the opposite way, that is, instead of turning yogurt into condensed form, by adding dry matter to the stirred yogurt, it becomes thick and thick. Abstract, and considering that these dry ingredients cause an unpleasant mouthfeel, therefore, adding a replacement such as transglutaminase enzyme can be important because this enzyme creates a network and increases viscosity by hydrolyzing protein, and also compared to adding dry ingredients, it can create more favorable sensory properties, which we investigate in this research. In addition, the addition of transglutaminase reduces the cost of producing the product compared to the addition of dry matter (Sanli et al, 2011).