Inulin and Fructooligosaccharide) on Quality Attributes Of
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Food Sci. Technol. Res., 15 (6), 605–612, 2009 Effects of Prebiotics (Inulin and Fructooligosaccharide) on Quality Attributes of Dried Yoghurt (Kurut) * A. Kemal SEÇKIN, Bülent ERGÖNÜL , Halil TOSUN and Pelin GÜNÇ ERGÖNÜL Celal Bayar University, Engineering Faculty, Food Engineering Department, Muradiye, Manisa, Turkey Received August 20, 2008; Accepted July 24, 2009 Chemical and microbiological attributes of prebiotic kurut were investigated. Prebiotic kurut was obtained by adding inulin and fructooligosaccharide into strained yoghurt. Chemical attributes and mi- crobiological analysis like total mesophylic aerobic bacteria, yeast and mold, lactic acid bacteria and total coliform bacteria counts were determined. Textural analyses of kuruts were also performed by texture analyzer. It was determined that using different amounts and types of polysaccharides in formulation did not affect the pH and aw values, salt, ash, protein, water, fat and cholesterol contents and acidity values of the samples (p>0.05). Also, firmness values, total mesophylic aerobic bacteria, lactic acid bacteria and co- liform counts of kurut samples were not affected by using added polysaccharides in formulation (p>0.05), whereas total yeast and mould counts of kuruts were affected by the formulation (p<0.05). Keywords: dried yoghurt, inulin, oligofructose Introduction to be dried. Final moisture content of Kurut varies from 10 Removal of water from foodstuff by drying is a widely to 20%. Dried yoghurt requires less packaging and storage known process since ancient times. Freeze drying, spray costs become of reduction of bulk and no refrigeration is re- drying, microwave drying, centrifugation, ultrafiltration and quired. concentrating under vacuum are the most known drying Prebiotics have been defined as selective non-digestible methods. Among these methods, drying foods under sun, is carbohydrate food sources that promote the proliferation of one of the cheapest and easy way to lengthen the shelf life. bifidobacteria and lactobacilli. So recently in food industry Dried food can be kept without any spoilage for long times. prebiotics began to be used because of their health benefits Since microorganisms need water to grow and multiply, dry- (Aryana and McGrew, 2007; Gibson and Roberfroid, 1995). ing also inhibits the growth of the microorganisms (Kumar Inulin is a blend of fructose polymers found in nature as and Mishra, 2004). plant storage carbohydrates. Oligofructose is a subgroup of Primary objective of drying yoghurt is to preserve it in inulin consisting of polymers with a degree of polymeriza- a shelf-stable dried form of high quality without a need for tion <10 (Aryana and McGrew, 2007; Niness, 1999). Both refrigeration. Dried yoghurt (Kurut) is a traditional dried yo- inulin and oligofructose are not digested in the upper gas- ghurt product made in Eastern region of Turkey. Especially trointestinal tract and do not lead to a rise in serum glucose Kurut is known as a winter food, since it is manufactured in nor stimulate insulin secretion (Aryana and McGrew, 2007; summer seasons to be consumed in winter in this region. It Niness, 1999). is made from yoghurt or ayran in Anatolia. In production of Oligofructose and inulin have health benefits like improv- Kurut, salt is added into yoghurt and salty yoghurt is strained ing bioavailability of calcium, magnesium and iron, increas- for 12 hours and typical Kurut dough is obtained. Then, ing activity of beneficial probiotic microorganisms, inhibit- dough is given shape as lumps of 40-60 g in weight and 3-5 ing the harmful bacteria in digestion system. Inulin decreases cm in diameter. Kurut lumps are set aside in a shady place fat absorption, helps digestion in high-protein diets, helps the body to eliminate toxins, lowers blood cholesterol and de- *To whom correspondence should be addressed. creases the risk of colon cancer (Aryana and McGrew, 2007; E-mail: [email protected] Jenkins et al., 1999). According to Chen et al. (2004), adding 606 A. K. SEÇKIN et al. prebiotics into milk increases the concentrations of amino lumps of 40-60 g and 3-5 cm in diameter were obtained by acids and organic acids in yoghurt by increasing the activity giving shape to strained yoghurt. Lumps were left in a shady of probiotic microorganisms. place for 11 days. Ipsen et al. (2001) reported that inulin improves the tex- Methods Water amount of Kurut was determined ac- tural and sensorial characteristics of yoghurt. Bozanic et al. cording to Association of Official Analytical Chemists (2001) found that the firmness of fermented goat and cow (AOAC) (1990). Total protein was determined by the Kjel- milks and yoghurts improved with the addition of inulin. dahl method. Protein was calculated using the general factor According to İbrahim et al. (2004), added inuline increased of 6.38 (AOAC, 1995). Fat and acidity values of samples the viscosity and curd tension of set fermented milk. Staf- were determined according to James (1995) pH value was folo et al. (2004) reported that yoghurt containing added determined by using a pH-meter (Hanna Instruments HI inulin had a stable color and water activity than the control 9321 Microprocessor). sample. Seydim et al. (2005) stated that inulin improves the Microbiological analyses were done according to IC- flavor of yoghurt and yoghurts containing added inulin have MSF (1986). For the detection of coliform microorganisms, a smoother texture than the others. samples were inoculated into tubes of Lauryl Tryptose Broth There is a limited literature indicating the chemical and (Oxoid, CM0451). Tubes were examined after overnight microbiological attributes of dried yoghurt. So, in this re- incubation at 37℃, and gas negative tubes were examined search, it was aimed to determine the chemical and micro- again after 48 h. Gas positive tubes were evaluated according biological attributes of prebiotic dried yoghurt which were to MPN (Most Probable Number) Table, and total coliform containing different amounts of fructooligosccharide and count per g of the sample was determined. Loopful inocu- inulin. lums of gas positive tubes were inoculated into tubes of Bril- liant Green Bile Broth (Oxoid, CM31) and Escherichia coli Material and Methods Broth (Oxoid, CM0990). Tubes were incubated at 44.5℃ for Kurut was manufactured in research laboratory of Celal 18 h. Durham tubes of Brilliant Green Bile Broth, in which Bayar University. Milk (3.5% fat) was purchased from a lo- turbidity and gas formation seen were signed as positive for cal market whereas milk powder was purchased from Pınar total coliform count. For E.coli test loopful inoculume of Milk Company, İzmir. Four different types of yoghurt were gas positive tubes of EC Broth were inoculated into poured manufactured for Kurut production. Fructooligosaccharide and dried plates of Eosin Methylene Blue Agar (Oxoid, and inuline were used as prebiotics. First of all milk powder CM0069). Typical colonies were isolated by a straight needle of 3% (w/v) was added in all samples. Sample containing into Tyrptone Water (Oxoid, CM0087) for indol test. only milk powder and containing no other additives, was Yeasts and moulds were enumerated by using Potato named as control sample (KC). Sample in which milk pow- Dextrose Agar (Oxoid, CM0139). pH adjusted to 3.5 by add- der (3%) and olygofructosaccahryde (3%) were added, was ing 10% (v/v) lactic acid after sterilization into media. Plates named as KO. Similarly, sample containing milk powder were incubated at 21℃ for 5 days, then yeast and mould (3%) and inuline (3%) was coded as KI. Also another sample colonies were counted. was prepared by adding milk powder (3%), fructooligosac- Total Mesophylic Aerobic Bacteria (TMAB) count of the charide (1.5%) and inulin (1.5%) into milk and was named samples was enumerated by using Plate Count Agar (Oxoid) as KOI. Fructooligosaccharide and inulin were added into and plates were incubated at 30℃ for 48-72 h. MRS Agar milk at 25℃, and samples were pasteurized at 90˚ for 10 was used as the media for the determination of Lactic Acid min, then cooled down to 42-43℃. Bacteria count, whereas the incubation was performed at 35 Milk was inoculated with yoghurt culture that was a ± 1℃ for 3 days. Pink colonies were counted at the end of blend of Streptococcus salivarus subp. thermophilus and the incubation period. Lactobacillus delbrueckii subsp. bulgaricus at a rate of 1:1. Firmness of Kurut samples Kurut lumps (50 × 30 mm) For yoghurt fermentation, yoghurt (3% w/v) was added into were taken under analysis. One bite penetration test was milk and milk was left for fermentation at 42 ± 1℃ until the performed using the Texture Analyser (TA-TX -2000 Farnell, final pH of 4.7 was achieved. England) with the probe and operated at a crosshead speed of After fermentation, salt (3%) was added into yoghurt by 1 mm s–1 and penetration distance of 10 mm. stirring well. Salted yoghurt was transferred into a cotton Lipid extraction and preparation of fatty acid methyl es- cloth bag. The weave intensity was 15 × 22 fibers/cm2. ters Lipids were extracted with diethyl ether as described After removal of yoghurt serum by straining, strained by Renner (1993). Approximately 50 g of sample is grinded yoghurts were taken into large plates for kneading and then through mixing together with 6-8 g kieselguhr in order to Effects of Prebiotics on Quality Attributes of Dried Yoghurt 607 increase surface contact area and then mixed with 200 mL and 300 mL/min for air. The injection volume was 2 µL. diethyl ether. The mixture was blended for 1 min and then The concentration of cholesterol (C) in analyzed samples filtered. The filtered solution (diethyl ether-lipid extract) was was calculated according to the equation C = M × V × 2.5, concentrated using rotary evaporator (IKA Labortechnik, where M is the computed mass (nanograms) of the analyte in Sweden) at 45 ± 1℃.