Evaluation of the Nutritional Value of Functional Yogurt Resulting from Combination of Date Palm Syrup and Skim Milk
The objective of this study was to use date palm syrup as a part of water (v/v) used in reconstituting skim milk powder in processing yogurt with 14% total solids. Physical properties such as sensory characteristics and apparent viscosity were evaluated. To evaluate the nutritional value of yogurt, antioxidant values were monitored during storage and the sample which recorded the highest values would determine its chemical composition. In addition, some micronutrients (HCl-soluble minerals) and (folate and C vitamins) compared to plain yogurt. Results showed that yogurt enriched with 10% date syrup had a significant sweetness, recorded the highest antioxidant values, higher in HCl-soluble minerals and folate concentration compared to plain yogurt. It could be concluded that numerous health benefits beyond its nutritional value have been associated with consuming yogurt enriched with 10% date palm syrup.
The date palm (Phoenix dactylifera L.) is one of the major fruit trees
in Egypt (El-Assar et al., 2005). Its production
and consumption is growing continuously due to its therapeutic properties beside
its high nutritive value (Karagul et al., 2004).
Date fruit consumption is an important source of supplying mineral and vitamin
elements in a balanced nutrition regime (Al-Shahib and Marshall,
2003). Research proves that when dates are eaten alone or in mixed meals
with plain yogurt have low glycaemic indexes (Yousif et
al., 1996; Miller et al., 2003). The
good news is that consumption of dates may also benefit in glycaemic and lipid
control of diabetic patients (Miller et al., 2002,
2003). Lately, several therapeutic virtues are assigned
to the date palm and its derivatives. Date fruit has anti-tumor activity (Ishurd
and Kennedy, 2005), antioxidant and anti-mutagenic properties (Vayalil,
2002; Mansouri et al., 2005). The fruit has
been recommended in folk remedies for the treatment of various infectious diseases
and cancers (Duke, 1992). Dry date fruits are used in
Indian traditional medicine after child birth as immunostimulants (Puri
et al., 2000). Extracts of the dates provided to the women after
childbirth stimulate their immune system (Puri et al.,
2000). Aqueous date extract was also found to inhibit significant the lipid
peroxidation and protein oxidation in a dose-dependent manner (Al-Laith,
2007). Furthermore, Al-Shahib and Marshall (2003)
concluded that, in many ways, dates may be considered as an almost ideal food,
providing a wide range of essential nutrients and potential health benefits.
On the other hand, a polysaccharide isolated from dates presented an antitumor
activity (Ishurd and Kennedy, 2005). Extracts of the
pits date decrease quickly and meaningfully the women's wrinkles (Bauza
et al., 2002). Yogurt is most often flavored with fruit preserves
or other ingredients (Potter and Hotchkiss, 1995). Flavored
yogurts are made by adding fruit concentrates or flavored syrups to cultured
milk before or after incubation (Keating and White, 1990).
The aim of this study was using the date extract as a part of aqueous phase
used in reconstitute skim milk powder, processed yogurt and evaluate the nutritional
values of the new product.
MATERIALS AND METHODS
This study was conducted from July 2008 to June 2009 in Dairy Science Department laboratories, National Research Centre, Dokki Giza Governorate, Egypt. Skim milk powder (low heat, origin USA) was reconstituted in distilled water and left overnight at 4°C to allow full hydration. Dried date fruits from local market. Folin-Ciocalteu reagent and 2,4,6-Tris [2- pyridyl]-s-triazine (TPTZ) were obtained from Fluka Chem. Co (Buchs, Swizerland), 2,2-Diphenyl-1-picrylhydrazyl (DPPH) radical and the reagents, (S)-(-)-6-Hydroxy -2,5,7, 8-tetramethylchroman -2-carboxylic acid (TROLOX) from (Sigma, St. Louis, Mo. USA) and gallic acid from (MP Biomedicals. Inc. (Eschwege, Germany). Sarter: freeze dried culture of Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus salivarious subsp. thermophilus (1:1) were obtained from Chr. Hansens laboratories, Denmark.
Preparation of Date Palm Syrup (Aqueous Extract of Date Fruit/Date Juice)
Dried date fruits (500 g) were grinded with a mechanical set (to increase
surface area), infused in 1000 mL hot water then stirred for 2 h and allowed
to stand in a refrigerator overnight to fully extract. The raw date palm syrup
was extracted by squeezing the mixture through cheese cloths. The date fruit
extract was collected and used with different concentrates as a part of water
(2.0, 4.0, 6.0, 8.0 and 10% v/v) in reconstituted skim milk powder that prepared
of processing yogurt (Vayalil, 2002).
Determination Total Soluble Solids (TSS) of Prepared Date Palm Syrup (Brix°)
Total soluble solids in the raw date palm syrup were measured using an Abbe
Mark II digital refractometer (Leica Inc., Buffalo, NY) by placing 0.5 g syrup
on the lens and reading the sample for temperature corrected Brix.
Skim milk powder was reconstituted in distilled water including date palm
syrup to give 14% total solids. Reconstitute milk was heat treated at 90°C
for 10 min, then cooled to 43°C, starter was added at the rate of 3% and
incubated at 43°C for 4 h until coagulation occur and samples reached to
pH 4.3. Yogurt then refrigerated at 5°C for 12 day and subsequent analysis.
Plain yogurt was produced by the same procedure. Samples were duplicated.
Physical Properties of the Yogurt
Yogurt samples were served in plastic plates labeled with three-digit codes
from a random number table. The quality properties that were evaluated were
color, firmness, smoothness, taste, sweetness, sourness, flavor and overall
acceptance. The sensory scores of produced types of yogurt was done on a 9-point
hedonic scale with 1 = dislike extremely and 9 = like extremely.
Apparent Viscosity of Yogurt (cP.s)
Apparent viscosity was based on measuring resistance to a rotating spindle
(Brookfield Model DV III, Programmable rheometer) depends on time of shearing
and test samples were subjected to shear rate a spindle speed of 50 rpm and
spindle rotating velocities, at constant temperature (25°C) for 5 min. The
instrument was equipped with an 18 measuring head. Samples were allowed to relax
(more than 10 min) prior to measuring their viscosity. All apparent viscosity
measurements were expressed in cintipoise seconds (cP.s), performed in duplicate.
Monitor the Antioxidant Activity in Yogurt (14% TS) During Storage (0, 3,
6, 9 and 12 Days)
Determination of Total Phenols Content
The method of Zheng and Wang (2001) was followed
in determining the total phenol compounds in yogurt using Folin Ciocalteu Reagent
(FCR) and gallic acid as a standard solution. Aliquots (20 μL) of the diluted
extracts were mixed with 100 μL of Folin-Ciocalteu phenol reagent and 300
μL of 20% Na2CO3. The absorbance was read with a
SP-2000UV UV/V is spectrophotometer at 765 nm. The total phenol contents were
calculated from a standard curve of diluted gallic acid solution and expressed
as gallic acid equivalent in (GAE) mg/100 mL extract.
Measurement of DPPH Radical Scavenging Activity
The DPPH free radical scavenging activity of yogurt was assessed according
to the method mentioned at (Larrauri et al., 1998)
with some modifications. Briefly, 40 μL of the different blends of yogurt
samples were mixed with 2.9 mL of 0.1 mM DPPH solution in methanol and the absorbance
was measured at 517 nm. A standard curve was prepared for the reaction between
40 μL of Trolox solutions (0.5 mM) and DPPH the same as the samples. The
scavenging activity of the different samples were measured from the prepared
standard cure and expressed as μmoles Trolox Equivalents/100 mL sample
Measurement of the Ferric Reducing Antioxidant Power (FRAP)
The method of Benzie and Strain (1996) was followed
in determining the FRAP. Aliquots of 100 μL of blended yogurt samples were
mixed with 3 mL FRAP reagent and the absorbance of reaction mixture was measured
at 593 nm after incubation at 37°C for 10 min. FRAP values were obtained
from a standard curve prepared ferrous sulphate (FeSO4.7H2O)
solutions (0.1-3.0 mmol L-1) and data was expressed as mg Fe2+/100
mL (FRAP value). Sample recorded the highest antioxidant values during storage,
the nutritional value evaluated as chemical composition and some micronutrient
(HCl-soluble minerals) and (folate and C vitamins) compared to plain yogurt.
Chemical Composition of Yogurt
The pH, acidity, moisture, protein, fat and total solids of yogurt containing
date products were determined. The pH was measured using a Jonway 705 pH meter.
Titrable acidity was determined as lactic acid by titrating with 0.1 N NaOH
using phenolphthalein as an indicator. Total solids content was determined in
a laboratory oven at 105°C for 24 h and total protein was assayed by Kjeldahl
method (Ling, 1963).
Liquid High-Performance Chromatographic Determination of Water-Soluble Vitamins
(Vit. C and Folic Acid in Yogurt)
A weight of 5 g of prepared yogurt sample was stirred well with 70 mL of
0.02% EDTA in 2 N H2SO4. The blend was transferred quantitatively
to a 100 mL volumetric flask and the volume made to mark with 0.02% EDTA solution.
An aliquot of the blend was centrifuged at 7000x g for 5 rain, then analyzed
for vitamin C according to the HPLC method of Ilic and Ashoor
Determination of HCl-Soluble Mineral (K, Ca, Mg, P, Fe and Z) Concentrations
Minerals (K, Ca, Mg, P, Fe and Zn) content of the yogurt was determined
by atomic absorption spectrophotometer (Varian spectra AA 220) (Tamimea
et al., 1999).
Statistical analysis was performed by using the General Linear Model (GLM)
procedure of Statistical Analysis System (SAS, 1988).
The Least Significant Difference test (LSD) was used to test differences between
Physical Properties of the Yogurt
Yogurt has 10% date palm syrup recorded the highest sensory scores (Table
1) had 35.8° Brix level (SS).
Apparent Viscosity of Yogurt (cP.s)
The apparent viscosity of yogurt measured as function of shearing time showed
greater reduction of apparent viscosity with time of shearing. In yogurt made
from skim milk mixed with different concentrations of aqueous extract of date
fruit dry dates (2.0, 4.0, 6.0, 8.0 and 10%) apparent viscosity at initial stress
were 41, 37, 34, 33 and 30.0 cP.s whereas plain yogurt recorded 46.0 cP.s (Fig.
1). Apparent viscosity had a lower viscosity in increased date palm syrup
concentration. The apparent viscosity with time of shearing, were decreased.
There were significant differences between concentration at time 0.0, 0.5, 1,
1.5, 2 and 2.5 min. However, at 3 min no significant differences between the
concentrations were observed.
Determination the Antioxidant Activities in Yogurt During Storage
Total Phenols Content
Soluble phenolic content of yogurt made with skim milk-date palm syrup were
increased significantly (p<0.05) with increasing the concentration of date
palm syrup 2, 4, 6, 8 and 10% in yogurt produced whereas decreased by storage
time (0, 3, 6, 9 and 12 days) in the fixed concentration. Plain yogurt had 248
mg GAE/100 mL sample at zero day storage was decreased to 210 mg GAE/100 mL
sample at 12 days storage and yogurt -10% date syrup had 306 mg GAE/100 mL yogurt
sample at zero day was also decreased to 260 mg GAE/100 mL yogurt sample at
12 days storage (Fig. 2).
|| Average scores of sensory evaluation of yogurt enriched with
different concentrations (0-10%) date palm syrup
|9-point hedonic scale was used with 1: Dislike extremely and
9: Like extremely. Means within a column not followed by a common letter
are different (p≤0.05)
||The dependency of the apparent viscosity of yogurt (skim milk
mixed with different concentration of dry dates 14%TS pH 4.5) with the time
at a constant shearing for 25°C. Data were analyzed by SAS (t) test,
one-way ANOVA followed by LSD test (p≤0.05)
||Effect of storage time on phenolic compound content in milk
with different conc. of dry dates additives. Data were analyzed by SAS (t)
test, one-way ANOVA followed by LSD test (p≤0.05)
DPPH Radical Scavenging Activity
Results showed that scavenging capacities of yogurt was significantly increased
(p<0.05) with increasing the concentration of date palm syrup addition. Scavenging
capacities of yogurt 10% date palm syrup was 103.3 TE mg/100 mL at zero day
storage and values was decreased to 80.3 TE mg/100 mL at 12 days storage. Scavenging
capacities of plain yogurt was 68.9 TE mg/100 mL at zero day storage and decreased
to 40.0 TE mg/100 mL at 12 days storage (Fig. 3).
The Ferric Reducing Antioxidant Power (FRAP)
This antioxidant power was significantly increased (p<0.05) with increasing
the date palm syrup concentration in the yogurt and decreased with extent storage.
The antioxidant power of in yogurt-has 10% date palm syrup was 43.3 mg Fe2+/100
mL at zero day storage then decreased to 33.5 mg Fe2+/100 mL after
12 days storage. The antioxidant power of plain yogurt was 35.4 mg Fe2+/100
mL at zero day storage then reduced to 23.0 mg Fe2+/100 mL after
12 days storage (Fig. 4).
||Effect of storage time on antioxidant activity of using DPPH
method in milk with different conc. of dry dates additives. Data were analyzed
by SAS (t) test, one-way ANOVA followed by LSD test (p≤0.05)
||Effect of storage time on antioxidant power (FRAP value) using
FRAP method of milk with different conc. of dry dates additives. Data were
analyzed by SAS (t) test, one-way ANOVA followed by LSD test (p≤0.05)
From previous results yogurt-10% date palm syrup recorded the highest antioxidant
values after 12 days storage, so it was chosen as a new product (functional
yogurt) and evaluated its nutritional value comparing with plain yogurt.
Evaluation the Nutritional Values of Yogurt-10% Date Juice Compared with
Chemical Composition of the Chosen Yogurt-Date Sample Compared to Plain Yogurt
Means for chemical composition (pH, acidity, moisture, protein, fat and
total solids) of yogurt containing 10% date palm syrup and plain yogurt are
presented in Table 2. Addition of date palm syrup had decreased
protein content, acidity and moisture while increased total solids of the yogurt.
Determination Some Micronutrients: Vitamins and Minerals
A rapid, simple and reliable liquid chromatographic method had been developed
for the simultaneous determination of water-soluble vitamins in yogurt. Results
showed no significant difference in vitamin C concentration in both yogurts
whereas folate concentration had increased significantly (p<0.05) in yogurt-10%
date juice compared to plain yogurt (Table 3).
|| Chemical composition of yogurt containing 10% date juice
and plain yogurt
|All data are insignificant (p>0.05)
|| Vitamins contents of yogurt
|Folate (folic acid or folacin) is a water-soluble B9 vitamin.
Dissimilar superscripts at the same column are significant (p<0.05)
|| HCl-soluble mineral content (K, Ca, P, Mg, Fe and Zn) (ppm)
|Dissimilar superscripts at the same column are significant
The HCl-soluble mineral content (potassium, calcium, phosphours, manganese,
iron and zinc) in the plain yogurt sample were 1978, 1100, 1002, 155, 3.1 and
5.2 ppm whereas in yogurt-10% date juice were 3744, 1700, 1704, 360, 10.8 and
17.8 ppm, respectively with significant differences (p<0.05) as in Table
Participants found the sensory attributes of yogurt flavored with date palm
syrup to be very acceptable. Previous studies were obvious that date fruit extracts
significantly increased or decreased gastrointestinal transit (GIT) in mice
(Al-Qarawi et al., 2003) and that date fruit
extract had strong antioxidant and antimutagenic properties (Vayalil,
2002). Data presented in this study demonstrated that yogurt containing
10% date palm syrup had significantly higher sensory evaluation, higher taste
rating, higher sweetness rating compared to plain yogurt. The higher tasty and
sweet was related to the date syrup that contain a high percentage of carbohydrate.
Although, with increasing the extract of date fruit in yogurt caused leasing
in the apparent viscosity, the yogurt with 10% date syrup gave acceptable consistency
specially it was processed without stabilizer. The high levels of sugar bind
moisture effectively thus preserving the fruit by preventing bacterial growth
(Al-Shahib and Marshall, 2003).
Yogurt enriched with 10% date palm syrup had the highest total phenolics content,
hydrogen-donating capacity and the ferric reducing antioxidant power compared
to the other sample with all storage time. The antioxidant activity of date
fruits have also been assessed and reported by other researchers using different
methods. The predominant phenolics found in date fruits are very active as antioxidants
and the antiradical activity in dates was highly correlated to the phenolic
contents (Mansouri et al., 2005). The antioxidant
activity of the yogurt 10% date palm syrup was attributed to the presence of
phenolic compounds (Ishurd and Kennedy, 2005; Al-Laith,
Vitamins and minerals are classified as micronutrients which the body's daily
requirements. This concentrate of date palm syrup (10%) in yogurt was compared
with plain yogurt in both some major minerals and vitamins as a required nutritional
quality of the product that providing a wide range of potential health benefits.
The HCl-soluble mineral content of the yogurt-10% date juice was higher than
the plain yogurts. The new product was also rich in calcium that helps strengthened
bones and is particularly beneficial to young children to prevent rickets and
brittle and weak bones in adults. Adequate intake of calcium and other nutrients
from dairy has also been demonstrated to help reduce the risk of high blood
pressure (Miller et al., 2000). This yogurt was
also rich with potassium which regulates the water balance in the body and provides
the appropriate alkaloidal features for body fluids. In addition, to stimulating
the kidneys to expel toxic bodily wastes (Lindinger, 1995).
Potassium is not stored in the body and much is lost in perspiration, it must
be continually replenished. Yogurt with date palm syrup has large amount of
iron which controls the synthesis of hemoglobin in the red blood cells and ensures
an appropriate level of red cells in the blood (MacPhail,
2007). Zinc in new yogurt was also more than in plain yogurt. Zinc believed
to play a valuable role in the healing process, blood stability and mental functions
and in keeping a proper alkaline balance in the body (Hamrick
and Counts, 2008).
Yogurt enriched with 10% date palm syrup was exceedingly rich in folic acid.
Folic acid, a B9 vitamin is of great importance to pregnant women. The need
for folic acid thus rises significantly during pregnancy and the daily requirement
doubles (Goh and Koren, 2008). Folic acid plays a particularly
important role in cell division and in the formation of the genetic structure
of the cell (Calvet and Chadwick, 1994). It has become
clear that folate play important roles not only in the prevention of neural
tube defects (Czeizel and Dudas, 1992), but possibly
also in the etiology of cardiovascular diseases (Verhoef
et al., 1996) and cancer (Giovannucci et al.,
1993, 1998). Folate helps in the metabolism of several
amino acids (Shimakawa et al., 1997).
Date palm syrup provides unique functionality when used with milk in processing yogurt including sweetening, flavoring and increasing nutritional quality. Yogurt enriched with 10% date palm syrup has a smooth texture, mildly sour and pleasant flavor besides the abundance of nutritional values that provides lots of health benefits. The main benefit of the new product yogurt is that it provides more content of HCl-soluble mineral that we need to stay healthy. Phosphorus works with calcium to help with bone strength and growth, potassium that helps to keep your muscles working correctly and Zinc is important for cell growth and repair. Yogurt enriched with 10% date palm syrup is also a good source of folate that is increasing the chances of achieving nutritional recommendation. Numerous health benefits beyond its nutritional value have been associated with consuming yogurt enriched with 10% date palm syrup.
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