Consumers are becoming more interested in incorporating healthy foods into their diet (Hekmat & Reid, 2006). Fermented beverages make up an important contribution to the human diet in many countries because fermentation is an inexpensive technology, which preserves the food, improves its nutritional value and enhances its sensory properties (Gadaga et al., 1999). Probiotic dairy products are considered to have functional properties because the probiotic bacteria added to the regular fermentation cultures provide therapeutic benefits such as modification of the immune system, reduction in cholesterol, alleviation from lactose intolerance, faster relief from diarrhea, and restoration of a healthy vaginal microbiota (Reid, 2001; Reid et al., 2003). Probiotics are commonly incorporated into fermented dairy products worldwide among which yogurt is a popular delivery vehicle (Ng et al., 2011). Yogurt is a well known fermented dairy food, which is usually manufactured form cow’s milk with or without the addition of some natural derivatives of milk, and processes a gel structure that is the result of coagulation of the milk proteins by lactic acid produced by Streptococcus thermophilus and Lactobacillus bulgaricus (Robinson, 2003). Recently, there has been an increasing interest in the use of natural food additives and incorporation of health-promoting substances into the diet (Varga, 2006).
However, maintain a high level of viable probiotic cell count in yogurts throughout the shelf life, is not a simple task. Many factors influence the viability of probiotics in yogurts such as strain variation, acid accumulation, interaction with starter cultures, level of dissolved oxygen and hydrogen peroxide, and storage condition (Donkor et al., 2006; Kailasapathy et al., 2007).
Cereals can be used as fermentable substrates for the growth of probiotic microorgamisms. The main parameters that have to be considered are the composition and processing of the cereal grains, the substrate formulation, the growth capability and productivity of the starter culture, the stability of the probiotic strain during storage, the organoleptic properties and the nutritional value of the final product. Additionally, cereals can be used as sources of nondigestible carbohydrates that besides promoting several beneficial physiological effects can also selectively stimulate the growth of Lactobacilli and Bifidobacteria present in the colon and act as prebiotics (Charalampopoulos et al., 2002). Of other cereals, barley (Hordeum vulgare L.) is an important miscellaneous grain in Korea and a widely consumed cereal because of its dietary health benefits, ready availability, reasonable cost, and processing properties of products such as beer, barley teas, and baked products. Base on grain composition, barley is classified as waxy, non waxy type, high lysine, high β-glucan, and proanthocyanidin- free (Lee et al., 2010). Also, barley is mostly known for its high amount of dietary fiber such as β -glucan and also contains other important compounds such as arabinoxylan, tocol, and phenolic compounds (Holtekjølen et al., 2008). The U.S. Food and Drug Administration (FDA) allowed the labels of foods containing the soluble fiber from barley products to claim that the consumption of these foods may reduce the risk of coronary heart disease (FDA, 2006). Increased fiber such as β-glucan consumption has been linked to a decrease in serum cholesterol and glycemic index (Behall et al., 2004; Cavallero et al., 2002). The objective of this study was to investigate the effect of addition of barely on quality characteristics of set type yogurt during fermentation by Lactic acid bacteria.
MATERIALS AND METHODS
Sample preparation, Chemical properties and β-glucan compounds
Two hulless waxy barley cultivars, cvs. Daeanchal and Boseokchal, were obtained from Department of Rice and Winter cereal Crop, National Institute of Crop Science, Korea. The whole barley was grinding using a rotor mill (ZM 100; Retsch GmbH, Haan, Germany) equipped with a 0.5 mm screen and then barley flour were put into plastic bags and stored at -20°C until used.
Chemical properties (moisture, crude protein, and ash) of colored barely was determined using the standard method described by the association of official analytical chemicals (AOAC 44-15A, 46-30, 08-01, 1990). Starch and β-glucan compounds was measured using Megazyme kit (Megazyme, Wicklow, Ireland) by McCleary and Glennie-Holmes (McCleary & Glennie-Holmes, 1985).
Yogurt preparation with barley flour
The yogurt base was prepared by dissolving whole milk powder (Seoulmilk Co, Seoul, Korea) in water and sterilized at 95°C for 20 min. It was supplemented with oligosaccharide (CJ cheiljedang Co, Seoul, Korea) that was added 20% concentration into the yogurt. Barley flour was mixed in water and it was gelatinization and sterilization at 120°C for 15 min. Addition concentration of the barley flour into the yogurt base was 10 and 20%, respectively. Control was not added barley and oligosaccharide. As strains for the manufacture of yogurt, Lactobacillus bulgaricus KCTC 3635, Streptococcus thermophilus KCTC 3778 and Lactobacillus acidophilus KCTC 3145 were used in this study and obtained from the Korean collection for type culture (KCTC, Daejeon, Korea). L. bulgaricus, L. acidophilus, and S. thermophilus were grown in a MRS broth (Difco, Laboratories, Sparks, MD, USA) at 37°C. The cell density of activated cultures was approximately 108~109 CFU/mL levels and it were used as yogurt starter. Yogurt mixture was blended and start culture was inoculated into mixed yogurt mixture with 5% concentration. And then it was fermented during 15 hr at 42°C. The yogurt fermented by L. acidophilus, L. bulgaricus and S. thermophilus mixed culture was used for investigation.
Properties of yogurt preparation with barley flours
The yogurt pH was measured using pH meter (MP220, Mettler Toledo, UK) with a pH metric probe and brix was measured with saccharometer (Atago, Tokyo, Japan). Titrate acidity expressed the value of titration with standard alkaline on total acid amount of the sample. The pH, brix and titrate acidity of the samples was measured three times for each samples and then averaged, respectively. Color of the sample was measured by a color difference meter (Color JS 55; Color Technology System Co., Tokyo, Japan). The color was measured 3 times for each samples and then averaged. The numerical value of the color was expressed by Hunter L, a, and b values. Hunter L value indicates the lightness of the samples, a value indicates the +red/-green, and b value indicates the +yellow/-blue. Microbiological analysis was measured. A sample (10 g) was aseptically homogenized for 2 min in a sterile stomacher bag containing 90 mL of sterile 0.1% peptone water using a bag mixer® (Model 400, Interscience Co, France). Media for enumeration of the Lactic acid bacteria were prepared by MRS agar (Oxoid, Basingstoke, Hampshire, England). Plates were incubated at optimal temperature of bacteria for 72 hr and colony forming units (CFU) per gram were counted at a dilution of 30 to 300 CFU per plate. Experiments with each bacterial culture were conducted independently twice.
Statistical analysis
The experiment was designed as randomized block design with three replications. One-way analyses of variance were performed using SAS software (version 8.0, SAS Institute, Cary, NC) along with Duncan’s post hoc tests to compare differences among mean values. Mean values and standard errors of the mean (SEM) were reported, and the significance was defined at p<0.01.
RESULTS AND DISCUSSION
Chemical composition and β-glucan compounds
The chemical properties and β-glucan compound of the samples was shown in Table 1. The moisture, crude protein, starch, ash and β-glucan of Deanchal were 7.88, 6.16, 44.00, 2.16 and 2.35%, respectively. Crude protein, starch and β-glucan of Boseokchal were 12.17, 53.14, and 5.80% respectively. Starch contents of Daeanchal were shown tend to be lower. β-glucan content of Boseokchal was a higher score compared with Daeanchal. Cha et al.,(2012) reported that crude protein of naked, hulled and glutinous barley was 12.1, 11.9 and 12.6%, respectively and crude lipid, ash and total mineral contents were slightly decreased after germination. Lee et al., (2012) reported that β-glucan of Saessalbori, Saechalssalbori and Hinchalssalbori were 4.79, 4.14 and 4.61% , respectively.
Changes of chemical compositions of yogurt during fermentation
Effect of barley flour added on quality characteristics of yogurt during fermentation was investigated. The addition of barley flour has been shown to affect the fermentation efficacy of Lactic acid bacteria in yogurt. In this study, not only barley but also oligosaccharide addition contributes to high pH of yogurt (Table 2). pH of yogurt added barley flour (Daeanchal) with 0 and 20% were 6.66 and 6.40, respectively. Gee et al. (2007) reported that addition of highly concentrated barley beta-glucan had no significant effect on the ability of the starter cultures to ferment. Low pH (4.6) and glucono delta lacton accumulation had no effect on the survival of L. acidophilus strains (Ng, 2011). As a similar result, Farnworth et al. (2007) reported that the falls of the pH values were faster in the soybeverage than in milk. Our research indicated that pH of yogurt supplemented with barley flour tended to be lower than before addition.
Table 2.
Change in pH of yogurt added colored barley flours during fermentation.
| Samples | Con. (%) | pH | |||
|---|---|---|---|---|---|
| 0 h | 5 h | 8 h | 15 h | ||
| Controla | 6.77±0.02a | 6.73±0.04a | 6.24±0.01a | 5.59±0.01a | |
| Daeanchal | 0 | 6.66±0.01b | 5.18±0.01b | 4.99±0.01b | 4.76±0.01b |
| 10 | 6.50±0.01c | 4.28±0.01e | 4.13±0.01f | 3.91±0.01f | |
| 20 | 6.40±0.01e | 4.37±0.01d | 4.10±0.01g | 3.97±0.01g | |
| Boseokchal | 0 | 6.71±0.01b | 5.16±0.01b | 4.96±0.01c | 4.62±0.03c |
| 10 | 6.53±0.06c | 4.16±0.01c | 4.34±0.01e | 4.05±0.01e | |
| 20 | 6.44±0.01d | 4.67±0.01c | 4.47±0.01d | 4.09±0.01d | |
| SEMb | 0.015 | 0.010 | 0.003 | 0.006 | |
Titratable acidity of yogurt was increased by addition barley flour. Also, titratable acidity was similar result with pH of yogurt. Titratable acidity of yogurt added barley flour was higher compared with those of control (Table 3). Donkor et al. (2006) concluded that the decrease in L. acidophilus cell numbers in yogurts was the result of lactic acid and acetic acids accumulation. Moreover, Ng et al. (2011) reported that the level of organic acids was found to have a more pronounced effect on the strain’s variability than the pH value. Sahan et al. (2008) reported that use of β-glucan hydrocollidal composite in the manufacture of non-fat yogurt did not significantly influence pH, titratable acidity, acetaldehyde, volatile fatty acid and tyrosine contents at any storage time.
Table 3.
Change in titratable acidity of yogurt added barley during fermentation.
| Samples | Con. (%) | Titratable acidity | |||
|---|---|---|---|---|---|
| 0 h | 5 h | 8 h | 15 h | ||
| Control | 13.50±1.41c | 14.50±2.12d | 30.75±1.06d | 44.50±0.71c | |
| Daeanchal | 0 | 21.50±2.12a | 54.25±0.35c | 62.25±2.47c | 66.50±1.41a |
| 10 | 23.50±2.12a | 93.50±2.12a | 104.25±1.77a | 121.25±0.35a | |
| 20 | 31.75±1.77a | 96.25±1.77a | 108.50±2.83a | 128.25±8.13a | |
| Boseokchal | 0 | 19.75±2.47a | 55.50±4.24c | 64.50±0.71c | 66.50±14.85a |
| 10 | 20.50±0.71a | 70.75±1.06a | 74.00±5.66a | 112.25±2.47a | |
| 20 | 22.25±2.47a | 74.25±2.47a | 91.50±0.71a | 121.50±4.95a | |
| SEMa | 1.386 | 1.637 | 1.916 | 4.780 | |
Change in brix of yogurt added barley during fermentation are shown in Table 4. Brix of yogurt was decreased during fermentation by Lactic acid bacteria. Also, addition of oligosaccharide was decreased of brix of yogurt during fermentation. However, addition of barley flour was not influence on brix of yogurt during 5 hr fermentation. Hou et al. (2000) showed that concentration of sucrose, raffinose and stachyose decreased during fermentation, in spite of that concentration of the monosaccharides fructose, glucose and galactose increased. However, Farnworth et al. (2007) reported that fructose was the sugar most utilized and glucose, raffinose and stachyose were used much less by Lactic acid bacteria.
Table 4.
Change in brix of yogurt added barley flours during fermentation.
| Samples | Con. (%) | Brix | |||
|---|---|---|---|---|---|
| 0 h | 5 h | 8 h | 15 h | ||
| Control | 20.97±0.81a | 21.40±0.72a | 20.27±0.25a | 18.17±0.06a | |
| Daeanchal | 0 | 20.17±0.15ab | 18.83±1.23b | 17.80±0.46bc | 17.93±0.58ab |
| 10 | 21.00±0.70a | 18.47±0.32b | 17.73±0.12c | 17.77±0.21ab | |
| 20 | 21.10±0.36a | 18.67±0.15b | 18.33±0.25b | 18.37±0.21a | |
| Boseokchal | 0 | 20.83±0.68a | 17.73±0.65b | 17.83±0.35bc | 17.37±0.35b |
| 10 | 20.67±0.12ab | 18.48±0.59b | 17.60±0.35c | 17.40±0.10b | |
| 20 | 19.70±0.85b | 18.33±0.21b | 17.77±0.06c | 17.43±0.57b | |
| SEMa | 0.346 | 0.377 | 0.169 | 0.205 | |
Hunter color values and microbiological analysis of the yogurt added colored barley flour
Color contributes to measuring the quality of a food, which attracts the consumer and color from natural sources is determined by handling or processing (Hallagan et al., 1995). Changes in the Hunter color value of yogurt added barley flour are shown in Table 5. Lightness of yogurt added barley flour (Daeanchal) addition 0 and 20% were 83.25 and 69.83, respectively. Yogurt during fermentation by Lactic acid bacteria induced the color change of the samples. Lee et al. (2002) reported that Hunter L (Brightness) value of curd yogurt added with 3% maesil extracts was not significantly different from the control curd yogurt. However, in this research, addition of barley flour as cereal was to decrease lightness of yogurt. Table 6
Table 5.
Hunter color value of yogurt added barley flours during fermentation.
| Sample | Con (%) | Ferm. Time (hr) | L | a | b |
|---|---|---|---|---|---|
| Control | 0 | 83.22±0.02a | -3.15±0.01b | 3.71±0.03a | |
| 15 | 81.84±0.06b | -2.65±0.03a | 2.43±0.01b | ||
| Daeanchal | 0 | 0 | 83.25±0.04a | -2.57±0.01 | 6.00±0.01b |
| 15 | 83.02±0.02b | -2.55±0.02 | 7.43±0.09a | ||
| 10 | 0 | 74.45±0.05 | -0.68±0.01b | 10.57±0.07b | |
| 15 | 74.34±0.16 | -0.59±0.02a | 11.44±0.11a | ||
| 20 | 0 | 69.83±0.08 | -0.17±0.01b | 12.53±0.08b | |
| 15 | 69.88±0.22 | -0.12±0.02a | 13.20±0.20a | ||
| Boseokchal | 0 | 0 | 83.01±0.04b | -2.70±0.02b | 5.60±0.07b |
| 15 | 83.45±0.01a | -2.63±0.01a | 7.54±0.03a | ||
| 10 | 0 | 72.90±0.09 | -0.13±0.01b | 8.23±0.07b | |
| 15 | 70.94±0.03 | -0.06±0.02a | 9.86±0.02a | ||
| 20 | 0 | 68.70±0.05a | -0.26±0.01b | 8.93±0.05b | |
| 15 | 67.49±0.02b | 0.49±0.01a | 9.78±0.03a | ||
Table 6.
Effect of barley flours on the growth (Log CFU/g) of Lactic acid bacteria in yogurt during fermentation.
| Samples | Con. (%) | Lactic acid bacteria (log CFU/g) | |||
|---|---|---|---|---|---|
| 0 h | 5 h | 8 h | 15 h | ||
| Control | 7.48±0.03c | 7.79±0.13e | 8.15±0.17c | 8.71±0.04c | |
| Daeanchal | 0 | 7.49±0.02c | 9.07±0.04d | 9.22±0.02b | 9.00±0.21b |
| 10 | 7.87±0.04ab | 9.95±0.01a | 10.02±0.64a | 9.68±0.04a | |
| 20 | 7.90±0.01a | 10.10±0.01a | 9.42±0.01ab | 9.47±0.11a | |
| Boseokchal | 0 | 7.48±0.03c | 9.27±0.08cd | 9.57±0.14ab | 9.47±0.12a |
| 10 | 7.83±0.02b | 9.57±0.19b | 9.60±0.14ab | 9.15±0.01b | |
| 20 | 7.89±0.01ab | 9.39±0.01bc | 9.62±0.01ab | 9.61±0.01a | |
| SEM | 0.019 | 0.065 | 0.187 | 0.073 | |
Cereal fermentation processes are affected by characteristic variables such as fermentable substrates, nutriens, growth factors, minerals, efficacy of growth inhibiting principle, water contents, and amylolytic activity (Hammes et al., 2005). The original microbial population of the yogurt during 0, 5, 8, and 15 hr fermentation was 7.48, 7.79, 8.15, and 8.71 Log CFU/g, respectively. Lactic acid bacteria count of yogurt added oligosaccharides was higher than the control. Moreover, the addition of barley flour was to promote the proliferation of Lactic acid bacteria in yogurt. Oligosaccharide, such as lactulose, fructo-oligosaccharides, and trans galacto-oligosaccharies have received interested attention, especially because they have been shown to be effective in stimulating the growth of Bifidobacteria and Lactobacilli in human large intestine (Charalampopoulos et al., 2002). Moreover, cereals have higher content of some of the essential vitamins than milk, higher content of dietary fibre, and increased amount of minerals, especially phosphorus. Charalampopoulos et al. (2002) reported that the malt medium supported better cell growth than barley and wheat due to the increased amounts of maltose, sucrose, glucose, and fructose (approximately 15 g of total fermentable sugars) and free amino nitrogen (approximately 80 mg). Lactic acid bacteria can rarely convert starch into lactic acid. However, some strains of Lactobacillus and Streptococcus and do it (Prade et al., 2008). Vasiljevic et al. (2007) reported that the barley beta-glucan addition suppressed proteolytic activity more than that from oat. In our research, addition of barley flours added into the yogurt base may also have contributed to growth of Lactic acid bacteria. Moreover, authors considered that results are good source to development of fermented food with the grain.
