NUTRITIONAL, MICROBIOLOGICAL AND SENSORY EVALUATION OF DIFFERENT BRANDS OF YOGHURT IN UYO METROPOLIS

NUTRITIONAL, MICROBIOLOGICAL AND SENSORY EVALUATION OF DIFFERENT BRANDS OF YOGHURT IN UYO METROPOLIS

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ABSTRACT

Yoghurt is a fermented dairy product which is consumed as a dessert, snack or as a probiotic food drink and has been one of the dairy products patronized by consumers in the Uyo metropolis. The study was undertaken to assess the nutritional, chemical, microbiological and sensory qualities offour brands of yoghurt obtained from different supermarkets in Uyo, Akwa-Ibom state, Nigeria. These products were coded YB1, YB2, YB3 and YB4. The four brands of yoghurt differed significantly (P<0.05) in their nutritional composition and the chemical properties of the four brands of yoghurt.The yoghurt brands had no fibre at all, the protein content which ranged from 1.28 + 0.02%-3.02 + 0.04%, but were generally lower than the specified limit stated by The Dairy Council. The fat content which ranged from 0.55 + 0.03% to 2.12 + 0.03%, YB1 was categorized as non-fat yoghurt, while YB2, YB3 and YB4 were categorized as low fat yoghurt using USDA specifications. The carbohydrate content ranged from 8.22 + 0.21% to 15.14% + 0.09% which were within the acceptable limit of The Dairy Council.The caloric value ranged from 51.65 + 0.86kcal to 90.16 + 0.22kcal, in which YB2, YB3 and YB4 is within the acceptable limit of The Dairy Council except YB1. The titratable acidity of the four brands of yoghurt ranged from 0.60 + 0.05% to 1.00+ 0.05%. The pH of the four brands of yoghurt ranged from 3.90 to 4.60.The total viable bacteria count ranged from 3.20 x 104 to 4.70 x 104cfu/ml and the total fungi count also ranged from 1.60 x 103 to 6.60 x 103cfu/ml which were above the recommended standard of Codex Standard for Fermented Milks which permits no yeast or moulds or any other microorganism that is not part of the specified starter culture for the product. However, there were no lactic acid bacteria and coliforms present in any brands of the yoghurt.Some spoilage bacteria and fungi were isolated from the four brands of yoghurt which are deleterious on human health and their percentage prevalence frequencies were also determined for each yoghurt brand.The calcium content which ranged from 44.18 + 0.02mg/100ml to 271.057 + 58.05mg/100ml, which was within the acceptable limit, the potassium content ranged 18.60 + 0.02mg/100ml – 63.06 + 0.07mg/100ml which was lower than the specified limit of The Dairy Council, Vitamin A and Vitamin C were found in traces in the four brands of yoghurt and were generally below the specified standard.Sensory panel of 20 evaluated the four brands of yoghurt, of which YB1 and YB3 had the highest overall acceptability, while YB2 had the least overall acceptability.

Keywords: Chemical,Microbiological, Nutritional, Sensory, Uyo-Nigeria, Yoghurt.

CHAPTER ONE

1.1                                                       INTRODUCTION

1.2Background of the Study

Yoghurt is a fermented dairy product obtained through anaerobic fermentation of lactose in milk by relevant microorganisms most of which are classified as pro-biotic (Tull, 1996). Lactose in evaporated whole milk, skimmed milk or fresh cow’s milk is converted into lactic acid by a symbiotic bacterial culture of Streptococcus thermophilus and Lactobacillus bulgaricus growing at temperatures in the range of 40–45oC (Wood, 1985).

Since the 1960s there has been worldwide increase and development in the production of yoghurt. In 2001, more than 9 million tons of yoghurt were produced, mostly in Europe (6.6million tons) (IDF, 2002). However, it is becoming more popular in other parts of the world including Africa. Several factors account for the success of yoghurt: the fact that it is a natural drink, has good organoleptic characteristics (fresh, acidulated taste and characteristic flavour) and good nutritional value. It also has prophylactic and therapeutic properties (Roissart and Luquet, 1994). Many Nigerians consume yoghurt as a dessert, snack or as a pro-biotic food drink to aid digestion and to reestablish a balance within the intestinal micro-flora.

Yoghurt is a preferred dairy product in areas where people are prone to lactose-intolerance. It is preferred over milk because it contains lactic acid which is readily digested as compared to lactose in unfermented milk. Yoghurt is a good dietary source of calcium, magnesium, phosphorus and zinc which are important in physiological processes and their contribution to total phosphorus intake has been reported as 30-45% in western countries (Flynn and Cashman, 1997). It is a nutritiously balanced food containing all the nutrients present in milk but in a more assimilable form. Essential minerals are present in dairy products at various levels depending on the type of milk used, the technological treatments during production of dairy products and the accuracy of analysis.

Many researchers have advocated the consumption of some cultured dairy products such as yoghurt in the prevention and treatment of several diseases: prophylaxis against the treatment of gastrointestinal infection, management of lactose intolerance and of hypercholesterolemia, the prevention of neoplastic disease (Fernandes and Shahani, 1990) and treatment of antibiotic associated colitis. For these reasons probiotic organisms are increasingly incorporated into food as dietary adjuncts to help maintain a healthy microbial gastrointestinal balance and their availability in yoghurt has made it increasingly popular in many parts of the world. Adequate numbers of viable cells, namely the ‘therapeutic minimum’ needs to be consumed regularly for transfer of the ‘probiotic’ effect to consumers. Consumption should be more than 100g per day of bio-yogurt containing more than 106cfumL-1(Rybka and Kailasapathy, 1995). Survival of these bacteria during shelf life and until consumption is therefore an important consideration.

In many countries, yogurt is still manufactured using traditional procedures. Since the last world war, yogurt consumption has been steadily increasing not only in European countries, but also in the United States, enhancing its industrial-scale production. At present, new types of fermented milk are available, prepared by adding fruits or flavouring, enriched with vitamins or containing selected intestinal bacteria such as Lactobacillus acidophilus and several Bifidobacterium species (Puhan,1988). Addition of different fruit in yogurt manufacture has been attempted increasingly. The use of fruit in yogurt makes it more delicious. This product contains both the refreshing flavour of fruit and beneficial effect of yogurt. Fruit yogurt has more taste and pleasing flavour (Mahmoodet al., 2008). The different types of flavouring that used in the Fruit yoghurt manufacture are fruits, canned fruit, fruits preserves, miscellaneous fruit products and frozen fruits. The kind of flavourings and their concentration is usually regulated according to the international standard say by each country. According to the FAO/ WHO concentrations of fruit for fruit yoghurt are between 5 and 15% (Mahmoodet al., 2008).

Like any other food product, the quality of yoghurt is a key to its acceptability and marketability. One important aspect of the quality of yoghurt relates with the physical properties of the yoghurt gel which should possess a smooth textural character in the mouth during consumption, as well as a low tendency to serum separation during storage (Rieneret al., 2010). In other words, higher viscosity and greater water-holding capacity of yoghurt are essential. The pH and titratable acidity of the product are also important quality factors since they are responsible for its characteristic taste. Finally, the total nutritional value, sensory characteristics and microbial safety also determine acceptability of the product.

The pH and acidity of yoghurt are influenced by the activity of the microorganisms responsible in fermentation of the milk during yoghurt production. Most of the other quality factors mentioned are affected by the type of milk used in the manufacturing process, additives present in the product and manufacturing practices and conditions (Bonczaret al., 2002).Although yeasts are not involved in the fermentation of yoghurt, they are frequently associated with the spoilage of the final product. Due to the inherent low pH of yoghurt, the product acts as a selective environment for the growth of yeasts (Suriyarachchi and Fleet, 1981). It is not uncommon to find yeast populations of 103cells/ml or more in retail samples of either plain or fruit yoghurts (Fleet, 1990), appearing as contaminants from the processing equipment and to a lesser effect, from the fruit, honey and sugar used as additives during production.

However, when storage temperatures are abused, there is rapid growth of yeasts and spoilage is evident in excessive gas formation, off flavours and discolouration. Though yoghurt is acknowledged as a product with quite a short shelf life, few attempts have been made to preserve it over a longer period. This is especially true with plain yoghurts. Pasteurized and chemically preserved yoghurts exist in some areas and have much longer shelf life periods. Dzigbordi, (2011)

1.3                   Problem Statement

The quality of yoghurt available in Uyo market varies from one producer to another and so do not have equal benefits. Despite the ever growing popularity of yoghurt in Uyo metropolis which include plain yoghurt, yoghurt fortified with fruit (Apple) and soy yoghurt and is consumed as desserts or refreshing beverage drinks, These several kinds of yoghurt differ in their composition or nutritional value, sensory characteristics and microbiological quality since all yogurts are not made through the same manufacturing process.

The conventional yoghurt starter bacteria, Lactobacillus bulgaricus and Streptococcus thermophilus lack the ability to survive passage through the intestinal tract and consequently do not play a role in the human gut (Gililard, 1979). Hence, there is a need for manufacturers to incorporate probiotics such as Lactobacillus acidophilus and Bifidobacterium into yoghurt to add extra nutritional-physiological value needed by consumers.

Adequate information on the nutritional value and sensory quality of yogurt products are not fully known since the packaging of most yogurt brands lacks specific labeling that precisely represents the content and type, thereby averting investigation by consumers. Many yoghurt brands may contain lower concentration of probiotics and may not meet the required standards prescribed by regulatory bodies. Poor quality milk, unhygienic practices associated with the process and the use of “wild type” of starter culture give rise to poor grade (Younuset al., 2002).

1.4                   Justification

The investigation and assessment of the nutritional quality, microbial quality and sensory characteristics of four brands of yoghurts which include plain yoghurt, yoghurt fortified with fruit and soy yoghurt will provide information that can be used to enhance the quality of the products and safeguard health and wellbeing of yoghurt consumers.  This will also enable Nigerians make choices based on the quality of the products as this will expand the knowledge of yoghurt consumers to know if the nutritional composition of the yoghurt can provides consumers with the beneficial effect and therapeutic value needed

The database of information that will be provided by the results of this study will indicate whether the products meet the appropriate legal and labeling requirements and whether they are safe or not. Regulatory bodies in the country and manufacturers of the yoghurt will have a basis for either encouraging production of yoghurt or standardizing yoghurt by improving manufacturing and quality assurance practices in this regard.

1.5                   Objectives

This study is aimed at evaluating the nutritional quality and sensorial characteristics of different brands of yoghurts available in Uyo metropolis.

Specific Objectives

v    To determine the presence/concentration of probiotics contained in different yoghurt samples if it meets the required standards prescribed regulatory bodies.

v    To determine the microbiological quality of four brands of yoghurt if it is safe for consumption.

v    To determine the physico-chemical properties of the four brands of yoghurt in relation to its sensory characteristics.

v    To determine the presence/concentration of vitamins and minerals as it is associated with the health benefits derived from the consumption of yoghurt.






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