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Quality attributes of a heart healthy yogurt
ARTICLE IN PRESS
LWT 41 (2008) 537–544 www.elsevier.com/locate/lwt
Quality attributes of a heart healthy yogurt Olga Cuevaa, Kayanush J. Aryanaa,b, a
School of Animal Sciences, Louisiana State University Agricultural Center, Baton Rouge, LA 70803, USA Department of Food Science, Louisiana State University Agricultural Center, Baton Rouge, LA 70803, USA
b
Received 17 May 2006; received in revised form 12 April 2007; accepted 14 April 2007
Abstract The objective was to study the effect of heart healthy nutrients on the physico-chemical, microbiological and sensory characteristics of yogurt. Thiamine (vitamin B1), riboflavin (vitamin B2), niacin (vitamin B3), folic acid (vitamin B9), manganese and magnesium were added during mix preparation at 0%, 30%, 60% and 90% of their respective recommended dietary allowance (RDA). Fiber (Ceolus Fiber DF-17) was added at a constant rate of 176 g/7.570 kg yogurt mix in all the treatments. Total solids in the control were kept constant with non-fat dry milk. Incorporation of the heart healthy nutrients at the 30%, 60% and 90% RDA significantly decreased syneresis, pH, L*, a* values but significantly increased b* value. Product viscosity was significantly increased by the incorporation of the nutrients at 60% of their respective RDA’s. The incorporation of the above heart healthy vitamins and minerals at any of the studied rates in yogurts did not significantly affect flavor, appearance, body and texture and microbial counts of the product. Although there were subtle yet significant changes in instrumental color and viscosity these slight changes could not be detected by sensory evaluation. Yogurts can successfully be manufactured with the above heart healthy nutrients. r 2007 Swiss Society of Food Science and Technology. Published by Elsevier Ltd. All rights reserved. Keywords: Yogurt supplementation; Vitamins; Minerals; Quality characteristics
1. Introduction Cardiovascular diseases rank as America’s No. 1 killer, claiming the lives of nearly 39% of more than 2.4 million Americans who die each year (Heart Facts, 2005). Direct medical cost of heart disease was $195 billion in 2001 (Seki & Cheng, 2003). Evidence is accumulating that a prudent diet, especially one involving an increased intake of dietary fiber, may protect against hypercoagulability (a state in which an alteration of the blood shifts the hemostatic balance toward excessive platelet/fibrin deposition leading to arterial and/or venous thrombosis) (Vorster et al., 1988). Men who ate more than 25 g of fiber per day had a 36% lower risk of developing heart disease, and those consumCorresponding author. School of Animal Sciences and Department of Food Science, Louisiana State University Agricultural Center, 115 Dairy Science Building, Baton Rouge, LA 70803, USA. Tel.: +1 225 578 4380; fax: +1 225 578 4008. E-mail address: [email protected] (K.J. Aryana).
ing 29 g of fiber per day decreased their risk of a heart attack by 41% (Wardlaw, 1999). An adult’s daily dietary fiber intake should generally fall in the range of 20–35 g/ day (Anonymous, 2004). Dairy products are not a good source of fiber. Incorporation of too much fiber deteriorates the quality of dairy products. Preliminary experiments in our laboratory indicated that about 5 g of fiber per 228 g cup of yogurt resulted in acceptable quality yogurt (unpublished results). Some experts suggest that adequate folate concentrations could prevent 56,000 cardiovascular deaths each year in the United States (Wardlaw, 1999). A high dose of oral folate acutely lowers blood pressure and enhances coronary dilation in patients with coronary disease (Tawakol et al., 2005). Vasarhelyi (1942) reported the disappearance of previously existing disturbances in carbohydrate and purine metabolism, decreased lactic and adenylic acid contents of the heart musculature, improved metabolism, diminished permeability of cells to thyroid hormone, increased acetylcholine levels, and increased glycogen content of
0023-6438/$30.00 r 2007 Swiss Society of Food Science and Technology. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.lwt.2007.04.002
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O. Cueva, K.J. Aryana / LWT 41 (2008) 537–544
liver and heart musculature after thiamin administration. The effect of riboflavin on the recovery of cardiac function in patients with coronary artery disease was reported by Zuo, Zhou, Lu, Sun, and Li (1997). They found that riboflavin was beneficial to systolic and diastolic function and stroke volume was significantly increased after oral administration of riboflavin (75 mg/day) for 30 days (Zuo et al., 1997). Controlled clinical studies have shown that niacin therapy effectively increases HDL and lowers triglyceride and LDL levels while causing a shift toward larger, less atherogenic LDL particles (Ito, 2003). The intake of dietary magnesium is associated with a reduced risk of coronary heart disease (Abbott et al., 2003). Other possible benefits of magnesium in relation to heart disease include decreasing blood pressure by dilating arteries, preventing heart rhythm abnormalities, and inhibiting blood clotting (Wardlaw, 1999). Manganese is a cofactor for certain enzymes, including pyruvate carboxylase, an enzyme used in carbohydrate metabolism and superoxide dismutase, an antioxidant enzyme (Greger & Malecki, 1997). Recommended intakes of folic acid, thiamin, riboflavin, niacin, magnesium and manganese are 400 mg, 1.2, 1.3, 16, 420, 2 mg/day, respectively (National Academy of Sciences, 1997). Achanta Aryana and Boeneke (2007) studied the characteristics of fat free plain set yogurts fortified with seven different minerals separately into yogurts. They observed no significant differences in viscosity, flavor and appearance in mineral fortified yogurts compared to control. They further better water holding capacities for yogurts with iron, selenium and magnesium compared to control. Yogurt is a popular dairy product that can be consumed as a dessert or a snack. Yogurt has gained wide popularity especially among women, children and teenagers who consume yogurt as part of their daily diet (Hekmat & McMahon, 1997). Yogurt consumption has steadily increased over the last 30 years in the United States (USDA, 2002). The healthy image associated with yogurt and other dairy products has led to the increase in consumption. It is advantageous to use yogurt as a vehicle for supplementing the diet with heart healthy nutrients. The objective of this study was to elucidate the effect of heart healthy nutrients at 0%, 30%, 60% and 90% of their respective recommended dietary allowance (RDA) on the physico-chemical, microbiological and sensory characteristics of plain yogurt over its shelf life. 2. Materials and methods 2.1. Experimental design Heart healthy plain yogurts were manufactured with thiamine (vitamin B1), riboflavin (vitamin B2), niacin (vitamin B3), folic acid (vitamin B9), manganese and magnesium incorporated at 0%, 30%, 60% and 90% of
their respective RDA. Fiber was incorporated at a constant rate of 176 g/7.570 kg yogurt mix in all the treatments since the amount of fiber would directly affect characteristics, such as viscosity, flavor and syneresis. The total solids in the control (no fiber, vitamins or minerals) were kept equal with the other yogurts by adding non-fat dry milk. Viscosity, syneresis, pH, color, microbial counts of the yogurts were determined and the sensory (flavor, body and texture, appearance and color) evaluation was conducted at days 1, 7, 21 and 34 after yogurt manufacture. 2.2. Yogurt manufacture Heart healthy plain yogurt was manufactured according to standard procedure at the Louisiana State University Dairy Processing Plant. Yogurt mixes were prepared in 7.570 kg batches from fluid skim milk with 681 g non-fat solids. Non-fat dry milk was added to the control at 455 g of the mix. In the treatments, the non-fat dry milk was added at 279 g and the fiber (Ceolus Fiber DF-17), (Matsutani Chemical Industry, Co., Ltd., Itami, Japan) was added at 176 g to keep the added solids constant at 455 g as in the control. Thiamine (vitamin B1), riboflavin (vitamin B2), niacin (vitamin B3), folic acid (vitamin B9), manganese and magnesium were obtained from Wright Nutrition, Inc., Crowley, LA. The weight of the yogurt mixes were 7.57 kg. These vitamins and minerals were incorporated in the yogurt mixes at 30%, 60% and 90% of their respective RDA’s per 228 g of yogurt (Table 1). In other words the yogurt mixes contained, 14, 28 and 42 mg of thiamine, 14, 28 and 42 mg of riboflavin, 169, 338 and 507 mg of niacin, 4.3, 8.6 and 12.9 mg of folic acid, 63.5, 127 and 190.5 mg of manganese, 290, 580 and 870 mg of magnesium in the treatments. Previously weighed ingredients were mixed into non-fat milk and the mixes were heated to 60 1C, homogenized at 13.8 MPa at the first stage and 3.45 MPa at the second stage. Homogenized mixes were batch pasteurized at 85 1C for 30 min and then rapidly cooled using an ice water bath to 40 1C. Freshly thawed frozen culture concentrate of Streptococcus thermophilus and Lactobacillus delbrueckii ssp. Bulgaricus (CH-3, yogurt culture, Chr. Hansen’s Laboratory, Milwaukee, WI, USA) Table 1 Recipe for 30%, 60% and 90% of the recommended dietary allowances (RDA) of the respective vitamins and minerals per 7.57 kg of yogurt mix
Thiaminea (mg) Riboflavina (mg) Niacina (mg) Folic acida (mg) Manganeseb (mg) Magnesiumc (mg) a
30%
60%
90% RDA
14 14 169 4.3 63.5 290
28 28 338 8.6 127 580
42 42 507 12.9 190.5 870
Purity 99% on dried basis. Used in the form of manganese sulfate monohydrate—purity, Mn content 33%. c Used in the form of magnesium carbonate—purity, Mg content 43.5%. b
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2.3. Color The L*a*b* values were determined on yogurts at 8 1C using a Hunter MiniScans XE Plus, portable color spectrophotometer (Hunter Associates Laboratory Inc. Reston, VA, USA). The instrument was calibrated using the black and white standard tiles that came along with the instrument. The operating conditions were 101 observer, D65 illuminant and 45/0 sensor. An average of five values was taken per sample. 2.4. pH The pH of the yogurts at 8 1C was determined using an UltraBasic Benchtop pH Meter (Denver Instrument Company, Arvada, CO, USA) calibrated using commercial pH 4.00 and 7.00 buffer solutions. 2.5. Sensory evaluation Sensory evaluations were conducted using a five member experienced panel. The panelists had over 4 months of training in judging yogurts. Samples were provided to panelists in three digit random number coded plastic cups. Water was provided to panelists to rinse their palate between samples. Panelists were instructed not to talk during the sensory evaluation. The official American Dairy Science Association intercollegiate dairy products evaluation contest score card was used to evaluate flavor on a 1–10 point scale (10 ¼ no criticism), body and texture, as well as the appearance and color, on a 1–5 point scale (5 ¼ no criticism). 2.6. Syneresis The release of whey in the yogurt samples was measured by inverting a 300 g sample at 8 1C on a fine cheese cloth placed on top of a funnel. The quantity of whey collected in a graduated cylinder after 2 h of drainage was used as an index of syneresis. 2.7. Viscosity The apparent viscosities were determined according to Farooq and Haque (1992). Apparent viscosities of yogurts at 8 1C were measured using a Brookfield DV II+ viscometer (Brookfield Engineering Lab Inc., Stoughton, MA, USA) with a helipath stand. A T-B spindle was used at 10 rpm. The data were acquired using the Wingathers software (Brookfield Engineering Lab Inc., Stoughton,
MA, USA). One hundred ten data points were averaged per replication. 2.8. Microbial counts Microbial counts were determined by plating serial dilutions of yogurt samples on MRS agar for lactic acid bacteria. Buffered peptone water (Difco, Detroit, MI, USA) was used for dilution blanks. The pour plates were incubated at 37 1C for 48 h under anaerobic conditions. 2.9. Statistical analysis Data were analyzed by analysis of variance using Proc Mixed of the Statistical Analysis Systems (SAS, 2004). Significant differences between means were determined using Fisher’s protected least significant difference test. Significant differences were determined at a ¼ 0.05. 3. Results and discussion 3.1. Physico-chemical characteristics 3.1.1. Viscosity Viscosity values are reported in Fig. 1. The treatment*day interaction effect was not significant (P ¼ 0.4661) but the treatment effect was significant (P ¼ 0.0109). The control was manufactured like a commercial control with fluid milk and non-fat dry milk. The treated yogurts containing nutrients for improved health had the same amount of added fiber as the added non-fat dry milk in the control to keep total solids constant in control and treatments. The yogurt containing vitamins and minerals incorporated at 60% of their RDA had significantly higher viscosities compared to the control.
30000 Apparent viscosity (cP)
was added at 5 ml per 7.57 kg of yogurt mixes. After mixing, the inoculated yogurt mixes were poured into 228 g plastic cups and incubated at 40 1C. Incubation was terminated at a pH of 4.5, which required approximately 3–4 h. The cups were refrigerated at 5 1C until analysis. Yogurt manufacture was replicated three times.
539
b b b a
a a
a b a
a
ab
ab
b
b a b
25000 20000 15000 10000 5000 0 Control
30% 60% Treatments
90%
Fig. 1. Apparent viscosity of yogurts supplemented with various levels of fiber, thiamine, riboflavin, niacin, folic acid, manganese and magnesium at day 1 , day 7 day 21 and day 34 of the yogurts with 0% (control), 30%, 60%, 90% of the RDA of the respective vitamins and minerals. abMeans for different treatments at the same storage time containing a common letter are not significantly (Po0.05) different from each other.
ARTICLE IN PRESS O. Cueva, K.J. Aryana / LWT 41 (2008) 537–544
540
Bienvenue, Jime´nez-Flores, and Singh (2003) reported that a gradual increase of added minerals resulted in a marked decrease in apparent viscosity in concentrated milk and an increase in viscosity of milk. Addition of ions (as sulfates or chlorides) into aqueous gelatin solutions (1–10%) at 0.15–0.50 mol/L increased viscosity of the solutions, gel strength, and decreased the time of gelation (Kozlov, Zholbolsynova, & Bekturov, 1984). Among the minerals used in the yogurts the maximum amount utilized was that of magnesium. The form of magnesium used was magnesium carbonate which had magnesium purity of 43.5%. Ohba, Yoshioka, and Takimoto (1999) manufactured a magnesium enriched dairy product using magnesium carbonate and reported that this milk product showed stability on thermal sterilization and storage. Nakata and Nanbu (2000) reported that the homogenized and sterilized slurry of Mg enriched reconstituted skim milk and butter did not result in any precipitate. The storage time significantly (Po0.0001) affected the viscosity. There were no significant differences between days 1 and 7. At day 21 the viscosity was the highest. Typically an increase in viscosity would suggest a decrease in syneresis probably because of more water being held within the product. 3.1.2. Syneresis The syneresis values are shown in Fig. 2. The treatment*day interaction effect was not significant (P ¼ 0.2770) but the treatment effect was significant (Po0.0001). The amount of syneresis in the control was significantly greater than the amount of syneresis in the treatments. Although total solids were kept constant, this decreased syneresis in the treatments probably can be ascribed to the improved water holding capacity of the fiber added to the treatments to make the healthy yogurts. The yogurts with vitamins and minerals added at 30% of their RDA had significantly 90
less syneresis than the yogurts containing vitamins and minerals added at 60% and 90% RDA and the control. Philippe, Le Graet, and Gaucheron (2004) studied the effect of different cations on the characteristics of casein micelles. They observed that the cations associated with the casein micelle in the following order Fe3+4Zn2+4 Ca2+4Cu2+4 Mg2+. They also reported changes in hydrophobicity and zeta potential of the casein micelles without any changes in micellar size. The storage period significantly (P ¼ 0.0350) affected the amount of syneresis. Although there were no significant differences between days 1, 7 and 34 the amount of syneresis at day 21 was significantly lower than the remaining weeks. In estimating shelf-life of concentrated yogurt, Al-Kadamany, Khattar, Haddad, and Toufeili (2003) reported that the degree of whey separation increased when increasing storage temperature from 5 to 15 and 25 1C, and these samples exhibited an initial increase followed by a marked decrease in syneresis towards the end of storage. 3.1.3. pH The pH values are illustrated in Fig. 3. The treatment*day interaction was not significant (P40.05). Both treatment and day effects were significant (P ¼ 0.0062 and 0.0033, respectively). The control had significantly higher pH than the treatments, but the yogurts with vitamins and minerals incorporated at 30%, 60% and 90% of their RDA’s were not significantly different from each other. Dello Staffolo, Bertola, Martino, and Bevilacqua (2004) studied the effects of different commercial dietary fibers (apple, wheat, bamboo or inulin) on sensory and rheological properties of yogurt and reported no significant differences for syneresis and pH among treatments. There were no significant differences between days 7, 21 and 34. The pH at day 1 was significantly the highest compared to days 21 and 34. The significant decline in pH
a a a a
4.7
80 c c c c
b b b b
b b b b
60
ab
ab
ab
b a
4.6
a b b
a b b
b
4.5
50 pH
Syneresis (ml)
70
a a a a
40
4.4
30
4.3
20
4.2
10
4.1
0 Control
30% 60% Treatments
90%
Fig. 2. Syneresis of yogurts supplemented with various levels of fiber, thiamine, riboflavin, niacin, folic acid, manganese and magnesium at day 1 , day 7 day 21 and day 34 of the yogurts with 0% (control), 30%, 60%, 90% of the RDA of the respective vitamins and minerals. abMeans for different treatments at the same storage time containing a common letter are not significantly (Po0.05) different from each other.
4.0 Control
30% 60% Treatments
90%
Fig. 3. pH of yogurts supplemented with various levels of fiber, thiamine, riboflavin, niacin, folic acid, manganese and magnesium at day 1 , day 7 day 21 and day 34 of the yogurts with 0% (control), 30%, 60%, 90% of the RDA of the respective vitamins and minerals. aMeans for different treatments at the same storage time containing a common letter are not significantly (Po0.05) different from each other.
ARTICLE IN PRESS O. Cueva, K.J. Aryana / LWT 41 (2008) 537–544
94.0
b b b b
b b b b
b b b b
93.0
L∗
92.5 92.0 91.5 91.0 90.5 90.0 Control
30% 60% Treatments
90%
Control
30%
90%
60%
0.0 -0.5 -1.0 -1.5 -2.0 -2.5
c c c c
b b b b
-3.0
ab ab
-3.5
ab ab
a a a a
Treatments d d d d
22 20
c c c c
18 b∗
3.1.4. L* The L* (lightness) values are reported in Fig. 4A. The treatment*day interaction was not significant (P40.05). Treatment was significant (P ¼ 0.0004). The L* value for the control was significantly higher than the L* value for the treatments. The L* values for yogurts with vitamins and minerals incorporated at 30%, 60% and 90% of their RDA’s were not significantly different from each other. Day was not significant (P ¼ 0.5467). In a study to elucidate effects of different commercial dietary fibers (apple, wheat, bamboo or inulin) on sensory and rheological properties of yoghurts, Dello et al. (2004) reported that only apple fiber yoghurt showed a color difference compared to the control.
a a a a
93.5
a∗
from day 1 to days 21 and 34 can be explained by lactose being fermented to lactic acid by the lactic acid bacteria (Kosikowski, 1982). Ibanoglu and Ibanoglu (1999) studied the effect of time and temperature on lactic acid fermentation of white flour–yogurt mixture. They reported a 5-fold reduction in fermentation time from 24.1 to 5.2 h when the temperature was increased from 20 to 40 1C. Bielecka, Maikowska, Biedrzycka, and Biedrzycka (2000) studied microbial changes in yogurts during manufacture and storage and reported a decrease in fermentation time with an increase in incubation temperature. Akin and Guler-Akink (2005) studied the effect of different incubation temperatures on the characteristics of yogurts. They reported that yogurts incubated at 37 1C had lower whey separation, titratable acidity and lactic acid contents and higher acetaldehyde content and viable bacterial counts compared to yogurts incubated at 42 1C. They concluded that lower temperature incubation could be satisfactorily used in yogurt manufacture.
541
b b b b
16 14
a a a a
12
3.1.5. a* The a* (red–green axis) values are presented in Fig. 4B. The a* values were negative implying that the values were in the green color space. Although the yogurts appeared white to the human eye/panelists, the instrument detected the green color. The treatment*day interaction and the day effect were not significant (P40.05), but the treatment was significant (Po0.0001). The control had significantly higher a* values compared to the treatments. The a* values of yogurts with vitamins and minerals added at 60% and 90% of their RDA were not significantly different from each other. The a* values of yogurts containing vitamins and minerals added at 90% of their RDA had significantly lower (higher on the negative scale) a* values than the control and the yogurts with vitamins and minerals incorporated at 30% RDA. The a* values were negative implying that they were in the green color space and the instrument detected greenness was increasing with an increase in vitamins and mineral content from 30% to 90% RDA.
10 Control
30% 60% Treatments
90%
Fig. 4. (a) L* (Lightness) values of yogurts supplemented with various levels of fiber, thiamine, riboflavin, niacin, folic acid, manganese and magnesium at day 1 , day 7 day 21 and day 34 of the yogurts with 0% (control), 30%, 60%, 90% of the RDA of the respective vitamins and minerals. abMeans for different treatments at the same storage time containing a common letter are not significantly (Po0.05) different from each other. (b) a* (redness–greenness) values of yogurts supplemented with various levels of fiber, thiamine, riboflavin, niacin, folic acid, manganese and magnesium at day 1 day 7 day 21 and day of the yogurts with 0% (control), 30%, 60%, 90% of the RDA of 34 the respective vitamins and minerals. abMeans for different treatments at the same storage time containing a common letter are not significantly (Po0.05) different from each other. (c). b* (yellowness–blueness) values of yogurts supplemented with various levels of fiber, thiamine, riboflavin, niacin, folic acid, manganese and magnesium at day 1 day 7 day 21 and day 34 of the yogurts with 0% (control), 30%, 60%, 90% of the RDA of the respective vitamins and minerals. abcdMeans for different treatments at the same storage time containing a common letter are not significantly (Po0.05) different from each other.
ARTICLE IN PRESS 4.7770.22a 4.3370.22a 4.5570.11a 4.5570.11a 5.0070.00 5.0070.00a 5.0070.00a 5.0070.00a Column means for a given parameter containing a common letter are not significantly (Po0.05) different from each other. a
8.0070.11 8.1170.11a 8.1170.29a 8.0070.19a
7.7770.29 7.6670.38a 7.2270.44a 7.6670.00a
7.7770.27 7.8870.21a 8.4470.39a 8.0070.11a
7.4470.29 7.1070.36a 7.4470.29a 7.5570.09a
4.4470.11 4.4470.11a 4.5570.23a 4.3370.44a
4.5570.11 4.6670.19a 4.7770.11a 4.3370.44a
4.5570.22 4.7770.22a 4.7770.21a 4.8870.11a
4.1170.23 4.4470.11a 4.1070.49a 4.5570.21a
4.8970.10 4.6670.13a 4.6670.13a 4.5570.22a
4.8970.11 4.8970.11a 5.0070.00a 5.0070.00a
a
21
a
7
a
1 21
a
34
a
a
7 1
a
21
a
34
a
Body texture scores at days
a
7
a
0 (Control) 30 60 90
3.2.3. Body and texture The body and texture scores are reported in Table 2. The treatment*day interaction was not significant (P ¼ 0.4638). Neither was the treatment effect significant (P ¼ 0.2232).
1
3.2.2. Appearance and color The appearance values are reported in Table 2. The appearance values in all the yogurts were above 4 on a scale of 1–5. The treatment*day interaction was not significant (P ¼ 0.5511). Neither was the treatment effect significant (P ¼ 0.6214) and nor was the day effect significant (P ¼ 0.3179). Although there was an increase in b* values these subtle yet significant differences detected by the instrument were not noticeable to the human eye. Yogurts being shrunken and/or lumpy also influence appearance, but none of these experimental yogurts were shrunken or lumpy.
Appearance scores at days
3.2.1. Flavor Flavor scores are illustrated in Table 2. The treatment*day interaction was not significant (P ¼ 0.3777). Neither was the treatment effect significant (P40.05). The maximum amount of mineral used was that of magnesium, which was in the magnesium carbonate form. Ohba et al. (1999) manufactured a magnesium enriched dairy product using magnesium carbonate and reported that this milk product showed stability on thermal sterilization and storage. Nakata and Nanbu (2000) reported that the homogenized and sterilized slurry of Mg enriched reconstituted skim milk and butter did not have any bitterness and tasted good. The storage time significantly (P ¼ 0.0003) affected the flavor. In general, the scores at day 34 were significantly lower than the other days. At day 34 the yogurts had reached their shelf life and the main criticism was high acetaldehyde and high acid. The high acid at day 34 corresponds to the lowest pH at day 34 (Fig. 3). Ferna´ndez Garcı´ a and McGregor (1997) observed evolution of organic acids in oat fiber-fortified yogurt during refrigerated storage for 4 weeks and reported significantly higher amounts of acetic and propionic acids in fortified yogurts.
Flavor scores at days
3.2. Sensory analysis
Treatments (% RDA)
3.1.6. b* The b* (yellow–blue axis) values are reported in Fig. 4C. The treatment*day interaction was not significant (P40.05). Storage time did not significantly (P ¼ 0.0523) affect the b* values, but treatment was significant (Po0.0001). The b* values of the control and all the treatments were significantly different from each other. The yogurt with vitamins and minerals incorporated at 90% of their RDA had the highest b* values. There was a steady increase in b* values with increase in addition of vitamins. This was because vitamins B2 and folic acid were yellow in color and a steady increase in addition of these vitamins resulted in a steady increase in yellowness.
34
O. Cueva, K.J. Aryana / LWT 41 (2008) 537–544 Table 2 Mean7SE of the flavor, appearance and color, and body and texture scores of the yogurts supplemented with 0%, 30%, 60% and 90% recommended dietary allowance (RDA) of, thiamine, riboflavin, niacin, folic acid, manganese and magnesium combined, over a storage period of 34 days
542
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a ab
360
106 cfu /g
310
a
260 210
a a
a b
a
a
b
a
a
a a
a a
160 110 60 10
0 (Control)
30%
60%
90%
Treatments Fig. 5. Microbial counts of yogurts supplemented with various levels of fiber, thiamine, riboflavin, niacin, folic acid, manganese and magnesium at day 1 day 7 day 21 and day 34 of the yogurts with 0% (control), 30%, 60%, 90% of the RDA of the respective vitamins and minerals. abMeans for different treatments at the same storage time containing a common letter are not significantly (Po0.05) different from each other.
Ferna´ndez Garcı´ a, McGregor, and Traylor (1998) concluded that fiber addition improved the body and texture of unsweetened yogurts but lowered overall scores for body and texture in yogurts sweetened with sucrose. The storage time significantly (Po0.0001) affected the body and texture. Body and texture scores for yogurts aged for 21 days were significantly higher than the yogurts at 1 and 34 days. Dello et al. (2004) reported that even though fibers modified certain rheological characteristics of the plain yogurt, the sensory properties were acceptable to panelists. Yogurts being grainy and/or ropy also influence body texture scores, but graininess or ropiness was not observed in the experimental yogurts. 3.3. Microbiological analysis 3.3.1. Microbial counts The microbial counts are presented in Fig. 5. The treatment*day interaction was not significant (P ¼ 0.3467). Neither was the treatment effect significant (P ¼ 0.1541). The storage time significantly (P ¼ 0.0022) affected the microbial counts. Microbial counts at day 7 were significantly higher than the microbial counts for the other weeks. There was no significant difference between microbial counts at days 1, 21 and 34. Microbial counts lowered significantly when the pH was 4.3 or lower (Lankaputhra, Shah, & Britz, 1996). In our case product pH was above 4.4 at the end of the 34th day of storage possibly explaining the high microbial counts of over 7 107 cfu/g. 4. Conclusion The incorporation of the heart healthy nutrients at 30%, 60% and 90% RDA significantly decreased syneresis, pH,
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L*, a* values and significantly increased b* values. Product viscosity was significantly affected by incorporation of the nutrients at 60% of their respective RDA’s. The incorporation of heart healthy nutrients to yogurts at any of the rates mentioned above did not significantly affect flavor, appearance, body and texture and microbial counts of the product. Storage time significantly affected syneresis, viscosity, pH, microbial counts, flavor, body and texture but did not significantly influence L* , a* and b* values. Heart healthy fat-free yogurts stored for 21 days had the highest viscosity, flavor, appearance, body texture and the least syneresis. Although incorporation of heart healthy nutrients affected some quality characteristics of fat free yogurts over its shelf life, these effects were not drastic. Heart healthy yogurts can be manufactured successfully.
References Abbott, R. D., Ando, F., Masaki, K. H., Tung, K., Rodriguez, B. L., Petrovitch, H., et al. (2003). Dietary magnesium intake and the future risk of coronary heart disease (The Honolulu Heart Program). American Journal of Cardiology, 92(6), 665–669. Achanta, K., Aryana, K. J., & Boeneke, C. A. (2007). Fat free plain set yogurts fortified with various minerals. LWT-Food Science and Technology, 40, 424–429. Akin, M. S., & Guler-Akink, M. B. (2005). Effect of different incubation temperatures on the microflora, chemical composition and sensory characteristics of bio-yogurt. Italian Journal of Food Science, 17(1), 64–67. Al-Kadamany, E., Khattar, M., Haddad, T., & Toufeili, I. (2003). Estimation of shelf-life of concentrated yogurt by monitoring selected microbiological and physicochemical changes during storage. Lebensmittel-Wissenschaft und – Technologie, 36(4), 407–414. Anonymous (2004). Herbal Fiberblend dietary fiber. Recommended fiber intake. Available: /http://www.allonhealth.com/dietary-fiber/dietaryfiber.htmS/[accessed 23 June 2005]. Bielecka, M., Maikowska, A., Biedrzycka, E., & Biedrzycka, El. (2000). Microbiological changes in modified yoghurts during manufacture and storage. Progress in Biotechnology, 17, 283–289. Bienvenue, A., Jime´nez-Flores, R., & Singh, H. (2003). Rheological properties of concentrated skim milk: Importance of soluble minerals in the changes in viscosity during storage. Journal of Dairy Science, 86, 3813–3821. Dello Staffolo, M., Bertola, N., Martino, M., & Bevilacqua, A. (2004). Influence of dietary fiber addition on sensory and rheological properties of yogurt. International Dairy Journal, 14(3), 263–268. Farooq, K., & Haque, Z. U. (1992). Effect of sugar-esters on the textural properties of non fat low calorie yogurt. Journal Dairy Science, 75, 2676–2680. Ferna´ndez Garcı´ a, E., & McGregor, J. U. (1997). Fortification of sweetened plain yogurt with insoluble dietary fiber. Zeitschrift fu¨r Lebensmittel-Untersuchung und -Forschung, 204(6), 433–437. Ferna´ndez Garcı´ a, E., McGregor, J. U., & Traylor, S. (1998). The addition of oat fiber and natural alternative sweeteners in the manufacture of plain yogurt. Journal of Dairy Science, 81, 655–663. Greger, J. L., & Malecki, E. A. (1997). Manganese: How do we know our limits? Nutrition Today, 32, 116. Heart Facts (2005). All Americans. CDC/NCHS. American Heart Association. Available: /www.americanheart.org/downloadable/ heart/1106668433197LatinoSpanHeartFacts05.pdf # search=‘Heart% 20Facts.%20%282004%29.%20All%20Americans.%20%20CDC% 20%2F%20NCHS.%20American%20Heart%20Association’S /[accessed 23 June 2005].
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Hekmat, S., & McMahon, D. (1997). Manufacture and quality of ironfortified yogurt. Journal of Dairy Science, 80, 3114. Ibanoglu, S., & Ibanoglu, E. (1999). Effect of time and temperature on lactic acid fermentation of a white wheat flour yoghurt mixture. Nahrung, 43(6), 414–417. Ito, M. K. (2003). Advances in the understanding and management of dyslipidemia: Using niacin-based therapies. American Journal of Health-System Pharmacy, 60(13, Suppl. 2), S15–S21. Kosikowski, F.V. (1982). Cheese and fermented milk foods (2nd ed.). Ithaca, NY. Kozlov, A. S., Zholbolsynova, A. S., & Bekturov, E. A. (1984). Effect of cobalt, nickel, copper, manganese, iron, and zinc ions on rheological properties of nutritive gelatin solutions. Izvestiya Akademii Nauk Kazakhskoi SSR, Seriya Khimicheskaya, 5, 36–39. Lankaputhra, W. E. V., Shah, N. P., & Britz, M. L. (1996). Survival of bifidobacteria during refrigerated storage in the presence of acid and hydrogen peroxide. Milchwissenschaft, 51, 65–70. Nakata, K., & Nanbu, H. (2000). Magnesium enriched food containing magnesium phosphates and surfactants. Japan Kokai Tokkyo Koho, 7. National Academy of Sciences (1997). United States Recommended Dietary Allowances. Available: /http://www.daily-vitamins.com/ rda.htmlS/[accessed 23 June 2005]. Ohba, T., Yoshioka, T., & Takimoto, M. (1999). Magnesium enriched dairy products and their manufacture. Japan Kokai Tokkyo Koho, 5.
Philippe, M., Le Graet, Y., & Gaucheron, F. (2004). The effects of different cations on the physicochemical characteristics of casein micelles. Food Chemistry, 90(4), 673–683. SAS. (2004). SAS user’s guide: Statistics, Version 9.1, Edition 2004. Cary, NC: SAS Inst., Inc. Seki, E., & Cheng, D. (2003). Major health care markets: By size and cost. The Biotechnology Review, 1–13. Tawakol, A., Migrino, R. Q., Aziz, K. S., Waitkowska, J., Holmvang, G., Alpert, N. M., et al. (2005). High-dose folic acid acutely improves coronary vasodilator function in patients with coronary artery disease. Journal of the American College of Cardiology, 45(10), 1580–1584. USDA (2002). Food consumption (per capita) data system. Economic Research Service. Available: /http://www.ers.usda.gov/data/ foodconsumptionS/[accessed 23 June 2005]. Vasarhelyi, B. (1942). Effect of vitamin B1 on heart and veins. Orvosi Hetilap, 86, 163–165. Vorster, H. H., Venter, C. S., Silvis, N., Van Eeden, T. S., Huisman, H. W., & Walker, A. R. P. (1988). Dietary influences on hemostasis may affect risk for coronary heart disease. South African Journal of Science, 84(5), 289–293. Wardlaw, G.M. (1999). Perspectives in nutrition (4th ed.). pp. 417–540. Zuo, B. H., Zhou, Z. Y., Lu, X. H., Sun, N., & Li, S. (1997). Effects of riboflavin on cardiac function and its mechanisms in patients with coronary artery disease. Zhongguo Bingli Shengli Zazhi, 13(2), 154–157.
LWT 41 (2008) 537–544 www.elsevier.com/locate/lwt
Quality attributes of a heart healthy yogurt Olga Cuevaa, Kayanush J. Aryanaa,b, a
School of Animal Sciences, Louisiana State University Agricultural Center, Baton Rouge, LA 70803, USA Department of Food Science, Louisiana State University Agricultural Center, Baton Rouge, LA 70803, USA
b
Received 17 May 2006; received in revised form 12 April 2007; accepted 14 April 2007
Abstract The objective was to study the effect of heart healthy nutrients on the physico-chemical, microbiological and sensory characteristics of yogurt. Thiamine (vitamin B1), riboflavin (vitamin B2), niacin (vitamin B3), folic acid (vitamin B9), manganese and magnesium were added during mix preparation at 0%, 30%, 60% and 90% of their respective recommended dietary allowance (RDA). Fiber (Ceolus Fiber DF-17) was added at a constant rate of 176 g/7.570 kg yogurt mix in all the treatments. Total solids in the control were kept constant with non-fat dry milk. Incorporation of the heart healthy nutrients at the 30%, 60% and 90% RDA significantly decreased syneresis, pH, L*, a* values but significantly increased b* value. Product viscosity was significantly increased by the incorporation of the nutrients at 60% of their respective RDA’s. The incorporation of the above heart healthy vitamins and minerals at any of the studied rates in yogurts did not significantly affect flavor, appearance, body and texture and microbial counts of the product. Although there were subtle yet significant changes in instrumental color and viscosity these slight changes could not be detected by sensory evaluation. Yogurts can successfully be manufactured with the above heart healthy nutrients. r 2007 Swiss Society of Food Science and Technology. Published by Elsevier Ltd. All rights reserved. Keywords: Yogurt supplementation; Vitamins; Minerals; Quality characteristics
1. Introduction Cardiovascular diseases rank as America’s No. 1 killer, claiming the lives of nearly 39% of more than 2.4 million Americans who die each year (Heart Facts, 2005). Direct medical cost of heart disease was $195 billion in 2001 (Seki & Cheng, 2003). Evidence is accumulating that a prudent diet, especially one involving an increased intake of dietary fiber, may protect against hypercoagulability (a state in which an alteration of the blood shifts the hemostatic balance toward excessive platelet/fibrin deposition leading to arterial and/or venous thrombosis) (Vorster et al., 1988). Men who ate more than 25 g of fiber per day had a 36% lower risk of developing heart disease, and those consumCorresponding author. School of Animal Sciences and Department of Food Science, Louisiana State University Agricultural Center, 115 Dairy Science Building, Baton Rouge, LA 70803, USA. Tel.: +1 225 578 4380; fax: +1 225 578 4008. E-mail address: [email protected] (K.J. Aryana).
ing 29 g of fiber per day decreased their risk of a heart attack by 41% (Wardlaw, 1999). An adult’s daily dietary fiber intake should generally fall in the range of 20–35 g/ day (Anonymous, 2004). Dairy products are not a good source of fiber. Incorporation of too much fiber deteriorates the quality of dairy products. Preliminary experiments in our laboratory indicated that about 5 g of fiber per 228 g cup of yogurt resulted in acceptable quality yogurt (unpublished results). Some experts suggest that adequate folate concentrations could prevent 56,000 cardiovascular deaths each year in the United States (Wardlaw, 1999). A high dose of oral folate acutely lowers blood pressure and enhances coronary dilation in patients with coronary disease (Tawakol et al., 2005). Vasarhelyi (1942) reported the disappearance of previously existing disturbances in carbohydrate and purine metabolism, decreased lactic and adenylic acid contents of the heart musculature, improved metabolism, diminished permeability of cells to thyroid hormone, increased acetylcholine levels, and increased glycogen content of
0023-6438/$30.00 r 2007 Swiss Society of Food Science and Technology. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.lwt.2007.04.002
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liver and heart musculature after thiamin administration. The effect of riboflavin on the recovery of cardiac function in patients with coronary artery disease was reported by Zuo, Zhou, Lu, Sun, and Li (1997). They found that riboflavin was beneficial to systolic and diastolic function and stroke volume was significantly increased after oral administration of riboflavin (75 mg/day) for 30 days (Zuo et al., 1997). Controlled clinical studies have shown that niacin therapy effectively increases HDL and lowers triglyceride and LDL levels while causing a shift toward larger, less atherogenic LDL particles (Ito, 2003). The intake of dietary magnesium is associated with a reduced risk of coronary heart disease (Abbott et al., 2003). Other possible benefits of magnesium in relation to heart disease include decreasing blood pressure by dilating arteries, preventing heart rhythm abnormalities, and inhibiting blood clotting (Wardlaw, 1999). Manganese is a cofactor for certain enzymes, including pyruvate carboxylase, an enzyme used in carbohydrate metabolism and superoxide dismutase, an antioxidant enzyme (Greger & Malecki, 1997). Recommended intakes of folic acid, thiamin, riboflavin, niacin, magnesium and manganese are 400 mg, 1.2, 1.3, 16, 420, 2 mg/day, respectively (National Academy of Sciences, 1997). Achanta Aryana and Boeneke (2007) studied the characteristics of fat free plain set yogurts fortified with seven different minerals separately into yogurts. They observed no significant differences in viscosity, flavor and appearance in mineral fortified yogurts compared to control. They further better water holding capacities for yogurts with iron, selenium and magnesium compared to control. Yogurt is a popular dairy product that can be consumed as a dessert or a snack. Yogurt has gained wide popularity especially among women, children and teenagers who consume yogurt as part of their daily diet (Hekmat & McMahon, 1997). Yogurt consumption has steadily increased over the last 30 years in the United States (USDA, 2002). The healthy image associated with yogurt and other dairy products has led to the increase in consumption. It is advantageous to use yogurt as a vehicle for supplementing the diet with heart healthy nutrients. The objective of this study was to elucidate the effect of heart healthy nutrients at 0%, 30%, 60% and 90% of their respective recommended dietary allowance (RDA) on the physico-chemical, microbiological and sensory characteristics of plain yogurt over its shelf life. 2. Materials and methods 2.1. Experimental design Heart healthy plain yogurts were manufactured with thiamine (vitamin B1), riboflavin (vitamin B2), niacin (vitamin B3), folic acid (vitamin B9), manganese and magnesium incorporated at 0%, 30%, 60% and 90% of
their respective RDA. Fiber was incorporated at a constant rate of 176 g/7.570 kg yogurt mix in all the treatments since the amount of fiber would directly affect characteristics, such as viscosity, flavor and syneresis. The total solids in the control (no fiber, vitamins or minerals) were kept equal with the other yogurts by adding non-fat dry milk. Viscosity, syneresis, pH, color, microbial counts of the yogurts were determined and the sensory (flavor, body and texture, appearance and color) evaluation was conducted at days 1, 7, 21 and 34 after yogurt manufacture. 2.2. Yogurt manufacture Heart healthy plain yogurt was manufactured according to standard procedure at the Louisiana State University Dairy Processing Plant. Yogurt mixes were prepared in 7.570 kg batches from fluid skim milk with 681 g non-fat solids. Non-fat dry milk was added to the control at 455 g of the mix. In the treatments, the non-fat dry milk was added at 279 g and the fiber (Ceolus Fiber DF-17), (Matsutani Chemical Industry, Co., Ltd., Itami, Japan) was added at 176 g to keep the added solids constant at 455 g as in the control. Thiamine (vitamin B1), riboflavin (vitamin B2), niacin (vitamin B3), folic acid (vitamin B9), manganese and magnesium were obtained from Wright Nutrition, Inc., Crowley, LA. The weight of the yogurt mixes were 7.57 kg. These vitamins and minerals were incorporated in the yogurt mixes at 30%, 60% and 90% of their respective RDA’s per 228 g of yogurt (Table 1). In other words the yogurt mixes contained, 14, 28 and 42 mg of thiamine, 14, 28 and 42 mg of riboflavin, 169, 338 and 507 mg of niacin, 4.3, 8.6 and 12.9 mg of folic acid, 63.5, 127 and 190.5 mg of manganese, 290, 580 and 870 mg of magnesium in the treatments. Previously weighed ingredients were mixed into non-fat milk and the mixes were heated to 60 1C, homogenized at 13.8 MPa at the first stage and 3.45 MPa at the second stage. Homogenized mixes were batch pasteurized at 85 1C for 30 min and then rapidly cooled using an ice water bath to 40 1C. Freshly thawed frozen culture concentrate of Streptococcus thermophilus and Lactobacillus delbrueckii ssp. Bulgaricus (CH-3, yogurt culture, Chr. Hansen’s Laboratory, Milwaukee, WI, USA) Table 1 Recipe for 30%, 60% and 90% of the recommended dietary allowances (RDA) of the respective vitamins and minerals per 7.57 kg of yogurt mix
Thiaminea (mg) Riboflavina (mg) Niacina (mg) Folic acida (mg) Manganeseb (mg) Magnesiumc (mg) a
30%
60%
90% RDA
14 14 169 4.3 63.5 290
28 28 338 8.6 127 580
42 42 507 12.9 190.5 870
Purity 99% on dried basis. Used in the form of manganese sulfate monohydrate—purity, Mn content 33%. c Used in the form of magnesium carbonate—purity, Mg content 43.5%. b
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2.3. Color The L*a*b* values were determined on yogurts at 8 1C using a Hunter MiniScans XE Plus, portable color spectrophotometer (Hunter Associates Laboratory Inc. Reston, VA, USA). The instrument was calibrated using the black and white standard tiles that came along with the instrument. The operating conditions were 101 observer, D65 illuminant and 45/0 sensor. An average of five values was taken per sample. 2.4. pH The pH of the yogurts at 8 1C was determined using an UltraBasic Benchtop pH Meter (Denver Instrument Company, Arvada, CO, USA) calibrated using commercial pH 4.00 and 7.00 buffer solutions. 2.5. Sensory evaluation Sensory evaluations were conducted using a five member experienced panel. The panelists had over 4 months of training in judging yogurts. Samples were provided to panelists in three digit random number coded plastic cups. Water was provided to panelists to rinse their palate between samples. Panelists were instructed not to talk during the sensory evaluation. The official American Dairy Science Association intercollegiate dairy products evaluation contest score card was used to evaluate flavor on a 1–10 point scale (10 ¼ no criticism), body and texture, as well as the appearance and color, on a 1–5 point scale (5 ¼ no criticism). 2.6. Syneresis The release of whey in the yogurt samples was measured by inverting a 300 g sample at 8 1C on a fine cheese cloth placed on top of a funnel. The quantity of whey collected in a graduated cylinder after 2 h of drainage was used as an index of syneresis. 2.7. Viscosity The apparent viscosities were determined according to Farooq and Haque (1992). Apparent viscosities of yogurts at 8 1C were measured using a Brookfield DV II+ viscometer (Brookfield Engineering Lab Inc., Stoughton, MA, USA) with a helipath stand. A T-B spindle was used at 10 rpm. The data were acquired using the Wingathers software (Brookfield Engineering Lab Inc., Stoughton,
MA, USA). One hundred ten data points were averaged per replication. 2.8. Microbial counts Microbial counts were determined by plating serial dilutions of yogurt samples on MRS agar for lactic acid bacteria. Buffered peptone water (Difco, Detroit, MI, USA) was used for dilution blanks. The pour plates were incubated at 37 1C for 48 h under anaerobic conditions. 2.9. Statistical analysis Data were analyzed by analysis of variance using Proc Mixed of the Statistical Analysis Systems (SAS, 2004). Significant differences between means were determined using Fisher’s protected least significant difference test. Significant differences were determined at a ¼ 0.05. 3. Results and discussion 3.1. Physico-chemical characteristics 3.1.1. Viscosity Viscosity values are reported in Fig. 1. The treatment*day interaction effect was not significant (P ¼ 0.4661) but the treatment effect was significant (P ¼ 0.0109). The control was manufactured like a commercial control with fluid milk and non-fat dry milk. The treated yogurts containing nutrients for improved health had the same amount of added fiber as the added non-fat dry milk in the control to keep total solids constant in control and treatments. The yogurt containing vitamins and minerals incorporated at 60% of their RDA had significantly higher viscosities compared to the control.
30000 Apparent viscosity (cP)
was added at 5 ml per 7.57 kg of yogurt mixes. After mixing, the inoculated yogurt mixes were poured into 228 g plastic cups and incubated at 40 1C. Incubation was terminated at a pH of 4.5, which required approximately 3–4 h. The cups were refrigerated at 5 1C until analysis. Yogurt manufacture was replicated three times.
539
b b b a
a a
a b a
a
ab
ab
b
b a b
25000 20000 15000 10000 5000 0 Control
30% 60% Treatments
90%
Fig. 1. Apparent viscosity of yogurts supplemented with various levels of fiber, thiamine, riboflavin, niacin, folic acid, manganese and magnesium at day 1 , day 7 day 21 and day 34 of the yogurts with 0% (control), 30%, 60%, 90% of the RDA of the respective vitamins and minerals. abMeans for different treatments at the same storage time containing a common letter are not significantly (Po0.05) different from each other.
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Bienvenue, Jime´nez-Flores, and Singh (2003) reported that a gradual increase of added minerals resulted in a marked decrease in apparent viscosity in concentrated milk and an increase in viscosity of milk. Addition of ions (as sulfates or chlorides) into aqueous gelatin solutions (1–10%) at 0.15–0.50 mol/L increased viscosity of the solutions, gel strength, and decreased the time of gelation (Kozlov, Zholbolsynova, & Bekturov, 1984). Among the minerals used in the yogurts the maximum amount utilized was that of magnesium. The form of magnesium used was magnesium carbonate which had magnesium purity of 43.5%. Ohba, Yoshioka, and Takimoto (1999) manufactured a magnesium enriched dairy product using magnesium carbonate and reported that this milk product showed stability on thermal sterilization and storage. Nakata and Nanbu (2000) reported that the homogenized and sterilized slurry of Mg enriched reconstituted skim milk and butter did not result in any precipitate. The storage time significantly (Po0.0001) affected the viscosity. There were no significant differences between days 1 and 7. At day 21 the viscosity was the highest. Typically an increase in viscosity would suggest a decrease in syneresis probably because of more water being held within the product. 3.1.2. Syneresis The syneresis values are shown in Fig. 2. The treatment*day interaction effect was not significant (P ¼ 0.2770) but the treatment effect was significant (Po0.0001). The amount of syneresis in the control was significantly greater than the amount of syneresis in the treatments. Although total solids were kept constant, this decreased syneresis in the treatments probably can be ascribed to the improved water holding capacity of the fiber added to the treatments to make the healthy yogurts. The yogurts with vitamins and minerals added at 30% of their RDA had significantly 90
less syneresis than the yogurts containing vitamins and minerals added at 60% and 90% RDA and the control. Philippe, Le Graet, and Gaucheron (2004) studied the effect of different cations on the characteristics of casein micelles. They observed that the cations associated with the casein micelle in the following order Fe3+4Zn2+4 Ca2+4Cu2+4 Mg2+. They also reported changes in hydrophobicity and zeta potential of the casein micelles without any changes in micellar size. The storage period significantly (P ¼ 0.0350) affected the amount of syneresis. Although there were no significant differences between days 1, 7 and 34 the amount of syneresis at day 21 was significantly lower than the remaining weeks. In estimating shelf-life of concentrated yogurt, Al-Kadamany, Khattar, Haddad, and Toufeili (2003) reported that the degree of whey separation increased when increasing storage temperature from 5 to 15 and 25 1C, and these samples exhibited an initial increase followed by a marked decrease in syneresis towards the end of storage. 3.1.3. pH The pH values are illustrated in Fig. 3. The treatment*day interaction was not significant (P40.05). Both treatment and day effects were significant (P ¼ 0.0062 and 0.0033, respectively). The control had significantly higher pH than the treatments, but the yogurts with vitamins and minerals incorporated at 30%, 60% and 90% of their RDA’s were not significantly different from each other. Dello Staffolo, Bertola, Martino, and Bevilacqua (2004) studied the effects of different commercial dietary fibers (apple, wheat, bamboo or inulin) on sensory and rheological properties of yogurt and reported no significant differences for syneresis and pH among treatments. There were no significant differences between days 7, 21 and 34. The pH at day 1 was significantly the highest compared to days 21 and 34. The significant decline in pH
a a a a
4.7
80 c c c c
b b b b
b b b b
60
ab
ab
ab
b a
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a b b
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Syneresis (ml)
70
a a a a
40
4.4
30
4.3
20
4.2
10
4.1
0 Control
30% 60% Treatments
90%
Fig. 2. Syneresis of yogurts supplemented with various levels of fiber, thiamine, riboflavin, niacin, folic acid, manganese and magnesium at day 1 , day 7 day 21 and day 34 of the yogurts with 0% (control), 30%, 60%, 90% of the RDA of the respective vitamins and minerals. abMeans for different treatments at the same storage time containing a common letter are not significantly (Po0.05) different from each other.
4.0 Control
30% 60% Treatments
90%
Fig. 3. pH of yogurts supplemented with various levels of fiber, thiamine, riboflavin, niacin, folic acid, manganese and magnesium at day 1 , day 7 day 21 and day 34 of the yogurts with 0% (control), 30%, 60%, 90% of the RDA of the respective vitamins and minerals. aMeans for different treatments at the same storage time containing a common letter are not significantly (Po0.05) different from each other.
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94.0
b b b b
b b b b
b b b b
93.0
L∗
92.5 92.0 91.5 91.0 90.5 90.0 Control
30% 60% Treatments
90%
Control
30%
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60%
0.0 -0.5 -1.0 -1.5 -2.0 -2.5
c c c c
b b b b
-3.0
ab ab
-3.5
ab ab
a a a a
Treatments d d d d
22 20
c c c c
18 b∗
3.1.4. L* The L* (lightness) values are reported in Fig. 4A. The treatment*day interaction was not significant (P40.05). Treatment was significant (P ¼ 0.0004). The L* value for the control was significantly higher than the L* value for the treatments. The L* values for yogurts with vitamins and minerals incorporated at 30%, 60% and 90% of their RDA’s were not significantly different from each other. Day was not significant (P ¼ 0.5467). In a study to elucidate effects of different commercial dietary fibers (apple, wheat, bamboo or inulin) on sensory and rheological properties of yoghurts, Dello et al. (2004) reported that only apple fiber yoghurt showed a color difference compared to the control.
a a a a
93.5
a∗
from day 1 to days 21 and 34 can be explained by lactose being fermented to lactic acid by the lactic acid bacteria (Kosikowski, 1982). Ibanoglu and Ibanoglu (1999) studied the effect of time and temperature on lactic acid fermentation of white flour–yogurt mixture. They reported a 5-fold reduction in fermentation time from 24.1 to 5.2 h when the temperature was increased from 20 to 40 1C. Bielecka, Maikowska, Biedrzycka, and Biedrzycka (2000) studied microbial changes in yogurts during manufacture and storage and reported a decrease in fermentation time with an increase in incubation temperature. Akin and Guler-Akink (2005) studied the effect of different incubation temperatures on the characteristics of yogurts. They reported that yogurts incubated at 37 1C had lower whey separation, titratable acidity and lactic acid contents and higher acetaldehyde content and viable bacterial counts compared to yogurts incubated at 42 1C. They concluded that lower temperature incubation could be satisfactorily used in yogurt manufacture.
541
b b b b
16 14
a a a a
12
3.1.5. a* The a* (red–green axis) values are presented in Fig. 4B. The a* values were negative implying that the values were in the green color space. Although the yogurts appeared white to the human eye/panelists, the instrument detected the green color. The treatment*day interaction and the day effect were not significant (P40.05), but the treatment was significant (Po0.0001). The control had significantly higher a* values compared to the treatments. The a* values of yogurts with vitamins and minerals added at 60% and 90% of their RDA were not significantly different from each other. The a* values of yogurts containing vitamins and minerals added at 90% of their RDA had significantly lower (higher on the negative scale) a* values than the control and the yogurts with vitamins and minerals incorporated at 30% RDA. The a* values were negative implying that they were in the green color space and the instrument detected greenness was increasing with an increase in vitamins and mineral content from 30% to 90% RDA.
10 Control
30% 60% Treatments
90%
Fig. 4. (a) L* (Lightness) values of yogurts supplemented with various levels of fiber, thiamine, riboflavin, niacin, folic acid, manganese and magnesium at day 1 , day 7 day 21 and day 34 of the yogurts with 0% (control), 30%, 60%, 90% of the RDA of the respective vitamins and minerals. abMeans for different treatments at the same storage time containing a common letter are not significantly (Po0.05) different from each other. (b) a* (redness–greenness) values of yogurts supplemented with various levels of fiber, thiamine, riboflavin, niacin, folic acid, manganese and magnesium at day 1 day 7 day 21 and day of the yogurts with 0% (control), 30%, 60%, 90% of the RDA of 34 the respective vitamins and minerals. abMeans for different treatments at the same storage time containing a common letter are not significantly (Po0.05) different from each other. (c). b* (yellowness–blueness) values of yogurts supplemented with various levels of fiber, thiamine, riboflavin, niacin, folic acid, manganese and magnesium at day 1 day 7 day 21 and day 34 of the yogurts with 0% (control), 30%, 60%, 90% of the RDA of the respective vitamins and minerals. abcdMeans for different treatments at the same storage time containing a common letter are not significantly (Po0.05) different from each other.
ARTICLE IN PRESS 4.7770.22a 4.3370.22a 4.5570.11a 4.5570.11a 5.0070.00 5.0070.00a 5.0070.00a 5.0070.00a Column means for a given parameter containing a common letter are not significantly (Po0.05) different from each other. a
8.0070.11 8.1170.11a 8.1170.29a 8.0070.19a
7.7770.29 7.6670.38a 7.2270.44a 7.6670.00a
7.7770.27 7.8870.21a 8.4470.39a 8.0070.11a
7.4470.29 7.1070.36a 7.4470.29a 7.5570.09a
4.4470.11 4.4470.11a 4.5570.23a 4.3370.44a
4.5570.11 4.6670.19a 4.7770.11a 4.3370.44a
4.5570.22 4.7770.22a 4.7770.21a 4.8870.11a
4.1170.23 4.4470.11a 4.1070.49a 4.5570.21a
4.8970.10 4.6670.13a 4.6670.13a 4.5570.22a
4.8970.11 4.8970.11a 5.0070.00a 5.0070.00a
a
21
a
7
a
1 21
a
34
a
a
7 1
a
21
a
34
a
Body texture scores at days
a
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a
0 (Control) 30 60 90
3.2.3. Body and texture The body and texture scores are reported in Table 2. The treatment*day interaction was not significant (P ¼ 0.4638). Neither was the treatment effect significant (P ¼ 0.2232).
1
3.2.2. Appearance and color The appearance values are reported in Table 2. The appearance values in all the yogurts were above 4 on a scale of 1–5. The treatment*day interaction was not significant (P ¼ 0.5511). Neither was the treatment effect significant (P ¼ 0.6214) and nor was the day effect significant (P ¼ 0.3179). Although there was an increase in b* values these subtle yet significant differences detected by the instrument were not noticeable to the human eye. Yogurts being shrunken and/or lumpy also influence appearance, but none of these experimental yogurts were shrunken or lumpy.
Appearance scores at days
3.2.1. Flavor Flavor scores are illustrated in Table 2. The treatment*day interaction was not significant (P ¼ 0.3777). Neither was the treatment effect significant (P40.05). The maximum amount of mineral used was that of magnesium, which was in the magnesium carbonate form. Ohba et al. (1999) manufactured a magnesium enriched dairy product using magnesium carbonate and reported that this milk product showed stability on thermal sterilization and storage. Nakata and Nanbu (2000) reported that the homogenized and sterilized slurry of Mg enriched reconstituted skim milk and butter did not have any bitterness and tasted good. The storage time significantly (P ¼ 0.0003) affected the flavor. In general, the scores at day 34 were significantly lower than the other days. At day 34 the yogurts had reached their shelf life and the main criticism was high acetaldehyde and high acid. The high acid at day 34 corresponds to the lowest pH at day 34 (Fig. 3). Ferna´ndez Garcı´ a and McGregor (1997) observed evolution of organic acids in oat fiber-fortified yogurt during refrigerated storage for 4 weeks and reported significantly higher amounts of acetic and propionic acids in fortified yogurts.
Flavor scores at days
3.2. Sensory analysis
Treatments (% RDA)
3.1.6. b* The b* (yellow–blue axis) values are reported in Fig. 4C. The treatment*day interaction was not significant (P40.05). Storage time did not significantly (P ¼ 0.0523) affect the b* values, but treatment was significant (Po0.0001). The b* values of the control and all the treatments were significantly different from each other. The yogurt with vitamins and minerals incorporated at 90% of their RDA had the highest b* values. There was a steady increase in b* values with increase in addition of vitamins. This was because vitamins B2 and folic acid were yellow in color and a steady increase in addition of these vitamins resulted in a steady increase in yellowness.
34
O. Cueva, K.J. Aryana / LWT 41 (2008) 537–544 Table 2 Mean7SE of the flavor, appearance and color, and body and texture scores of the yogurts supplemented with 0%, 30%, 60% and 90% recommended dietary allowance (RDA) of, thiamine, riboflavin, niacin, folic acid, manganese and magnesium combined, over a storage period of 34 days
542
ARTICLE IN PRESS O. Cueva, K.J. Aryana / LWT 41 (2008) 537–544
a ab
360
106 cfu /g
310
a
260 210
a a
a b
a
a
b
a
a
a a
a a
160 110 60 10
0 (Control)
30%
60%
90%
Treatments Fig. 5. Microbial counts of yogurts supplemented with various levels of fiber, thiamine, riboflavin, niacin, folic acid, manganese and magnesium at day 1 day 7 day 21 and day 34 of the yogurts with 0% (control), 30%, 60%, 90% of the RDA of the respective vitamins and minerals. abMeans for different treatments at the same storage time containing a common letter are not significantly (Po0.05) different from each other.
Ferna´ndez Garcı´ a, McGregor, and Traylor (1998) concluded that fiber addition improved the body and texture of unsweetened yogurts but lowered overall scores for body and texture in yogurts sweetened with sucrose. The storage time significantly (Po0.0001) affected the body and texture. Body and texture scores for yogurts aged for 21 days were significantly higher than the yogurts at 1 and 34 days. Dello et al. (2004) reported that even though fibers modified certain rheological characteristics of the plain yogurt, the sensory properties were acceptable to panelists. Yogurts being grainy and/or ropy also influence body texture scores, but graininess or ropiness was not observed in the experimental yogurts. 3.3. Microbiological analysis 3.3.1. Microbial counts The microbial counts are presented in Fig. 5. The treatment*day interaction was not significant (P ¼ 0.3467). Neither was the treatment effect significant (P ¼ 0.1541). The storage time significantly (P ¼ 0.0022) affected the microbial counts. Microbial counts at day 7 were significantly higher than the microbial counts for the other weeks. There was no significant difference between microbial counts at days 1, 21 and 34. Microbial counts lowered significantly when the pH was 4.3 or lower (Lankaputhra, Shah, & Britz, 1996). In our case product pH was above 4.4 at the end of the 34th day of storage possibly explaining the high microbial counts of over 7 107 cfu/g. 4. Conclusion The incorporation of the heart healthy nutrients at 30%, 60% and 90% RDA significantly decreased syneresis, pH,
543
L*, a* values and significantly increased b* values. Product viscosity was significantly affected by incorporation of the nutrients at 60% of their respective RDA’s. The incorporation of heart healthy nutrients to yogurts at any of the rates mentioned above did not significantly affect flavor, appearance, body and texture and microbial counts of the product. Storage time significantly affected syneresis, viscosity, pH, microbial counts, flavor, body and texture but did not significantly influence L* , a* and b* values. Heart healthy fat-free yogurts stored for 21 days had the highest viscosity, flavor, appearance, body texture and the least syneresis. Although incorporation of heart healthy nutrients affected some quality characteristics of fat free yogurts over its shelf life, these effects were not drastic. Heart healthy yogurts can be manufactured successfully.
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