Use of whey powder and skim milk powder for the production of fermented cream

Milk powder is a nutritious and stable product which is produced by vaporization of water from milk, condensation and powdering of dry matter (Üçüncü, 2005). Skim milk powder is used mostly in high protein-less fat content products because of its much stable structure. Whey is a green yellowish liquid remaining after coagulation process with acid or enzyme and it is a by-product of cheese and caseine production (Zadow, 1994).


Introduction
Fermented cream is a sour tasty fermented product obtained by acidification of pasteurized cream containing 10-40% fat (Esen, 1994).It is commonly consumed with characteristic aroma and flavour in many countries.Fermented cream with fat content of 10-15% and nonfat solid content of 14-18%, has a lower viscosity and its shelf life is approximately four weeks (Özdemir, 2002).
Milk powder is a nutritious and stable product which is produced by vaporization of water from milk, condensation and powdering of dry matter (Üçüncü, 2005).Skim milk powder is used mostly in high protein-less fat content products because of its much stable structure.Whey is a green yellowish liquid remaining after coagulation process with acid or enzyme and it is a by-product of cheese and caseine production (Zadow, 1994).
In this study the effect of enrichment of nonfat solid content with addition of demineralized whey powder and skim milk powder on some properties (total solid, ash, fat, titratable acidity, pH, total nitrogen, tyrosine, diacetyl, peroxide and acid number) of fermented cream were investigated.The main purpose of this study was about the enhancement of some properties of fermented cream by increasing the nonfat solid content.B2I: Fermented cream containing 4% 50% demineralized whey powder C1I: Fermented cream containing 2% 70% demineralized whey powder C2I: Fermented cream containing 4% 70% demineralized whey powder ControlI: Fermented cream without any powder addition

Determination of chemical and sensory properties
The total solid content of samples was determined by oven drying method.The fat content was determined by Gerber method and total nitrogen content was determined by Kjeldahl method (Gripon et al., 1975), the pH-value was measured using a pHmeter model Mettler Toledo (Analytical,Schwerzenback,Switzerland) and the non-fat-solid content was measured by refractometry (Atago hand held refractometer).Tyrosine and peroxide values were determined by spectrophotometric method (Hull, 1947;Downey, 1975); acid number was determined by titrimetric method (Hortwitz, 1965).Samples of fermented cream were analyzed by 7 panelists in the scope of sensory analyses according to the scoring card described by Bodyfelt et al. (1988).

Determination of viscosity
Viscosity values were measured by viscosimetry (Haake VT 181/VTR 24) with MV II heading.

Determination of diacetyl value
The quantity of diacetyl was measured by headspace method (Ulbert, 1991) using gas chromatography (Agilent 6890 Series, Agilent Tech., Inc, USA) equipped with a FID detector and 30 m x 320 µm i.d.polyethylene glycol capillary column with 0.25 µm film thickness.5 g of each fermented cream sample was weighted into headspace vials and capped with crimper.Samples were stored at -18 °C until they were used.Samples were held at 70 °C/30 min before injection to the GC.Injector block temperature was 80 °C and FID temperature was 250 °C.Flow rates of air, hydrogen and nitrogen (make up) were 400, 40 and 30 mL/min, respectively.

Statistical analysis
For the statistical analyses of results, randomized block design variance analysis method was used and Duncan multiple comparison test was applied to assess the differences between the averages (Düzgüneş et al., 1987).

Total solid, ash, pH and titratable acidity
Total solid content is one of the most substantial parameter in food industry.It effects food quality directly and it gives information about product composition (Reh & Gerber, 2003).It is also considered as indicator of nutrition value (Lindmark-Mansson et al., 2003).There was no difference between solid contents of samples during storage (p > 0.05).The total solid content of A1 was 26.00%; sample A2 was 27.05%; sample B1 was 26.25%; sample B2 was 27.38%; Sample C1 was 26.50%; sample C2 was 26.94% and control sample was 25.6%.
The results show that the addition of milk powder directly affected the solid content of fermented cream samples.The mean value of total solid content of control sample was 25% after the 29 th day of storage.The total solid content of control and skim milk powder added samples increased on the 8 th day of storage and it did not change afterwards.That was because, fermentation process continued until the 8th day and then it slowed down.
During the storage period, there was a small change in the fat ratio standardized at 18 ± 0.5% for the production of fermented cream samples but it wasn't statistically important and so was the dry matter change.
There was no significant difference between ash values in samples during storage and this was the same to solid contents.The total ash content of sample A1 was 0.67%; sample A2 was 0.72%; sample B1 was 0.64%; sample B2 was 0.74%; sample C1 was 0.67%; sample C2 was 0.74% and control sample was 0.55%.The ash values of the fermented cream samples were lower than the other dairy products because of ash reduction due to the increase in fat ratio (Milanović et al., 2008) in dairy products.
Mean values of titratable acidity and pH value of fermented cream samples are shown in Table 1.Titratable acidity changes showed similar differences in all samples.It was determined that titratable acidity of control sample was lower than the other samples.Titratable acidity of the samples added with skim milk powder was the highest of all samples.There was no significant effect of storage on titratable acidity (p > 0.05).But titratable acidity values of all samples were increased during storage.However there was significant difference between titratable acidity values of samples with skim milk powder added than the other samples (p < 0.05).According to this result, fermented cream samples with milk powder had increased lactic acid production because of high lactose content.

Total protein and tyrosine
Mean values of total nitrogen of fermented cream samples are presented in Figure 2.There was no significant difference between the samples (p > 0.05) except for the samples which contained skim milk powder (Sample A1 and A2) (p < 0.05).It is known that the ratio of total nitrogen of skim milk powder is more than that of whey powders.So nitrogen value increase by addition of skim milk powder.Samples A1 and A2 had the highest total nitrogen values.Total nitrogen values of samples decreased during the first 7 days of storage.It is known that demineralization process has no effect on protein content.Consequently there was no differences between samples of 50% (B1 and B2) and 70% (C1 and C2) of demineralized whey powder addition.Total nitrogen value increases with the increase of powder and the same applies with skim milk powder.
Tyrosine is an amino acid which has aromatic and bitter taste and it is known as 4-hydroxiphenilalanin or 2-amino-3-propanoic acid.The amount of tyrosine is considered as an indicator of proteolitic activity (Ersoy & Uysal, 2002).The tyrosine values of fermented cream samples were changed at a range of 0.116-0.121mg/g and the mean value of tyrosine of fermented cream samples added with milk powder and whey powder was 0.118 mg/g.There was no difference between tyrosine values of samples during storage (p > 0.05).

Peroxide and acid number
Mean values of peroxide and acid number of fermented cream samples are presented in Table 2.The acid number indicates the amount of free fatty acids in lipids and is calculated by measurement of KDH which is used to neutralize 1 gram of fat.Acid number is important because it is an indicator of degree of lipolysis.According to Table 2, acid numbers of all samples increased until the 15 th day of storage.Rancid taste was detectable when acid number was higher than 3.065 mg KDH in fermented cream with 18% fat ratio (Manav, 2011).
Dxidative deterioration in dairy products generally occurs as a result of unsaturated fatty acids otooxidation.Peroxide is a primary product of oxidation.Lipid reacts with oxygen which is contained in the product resulting into a rancid flavour (Bandyopadhyay et al., 2008).The results showed that peroxide values of all samples increased on the 8 th day of storage (Table 3) and it is seen that the peroxide values decreased after that date.This is because peroxide is unstable and it turns easily into a secondary oxidation product.In the following days of storage,   peroxide value decreased in all samples.This is because of the unstable nature of peroxide whereby the primary oxidation occurs rapidly into secondary oxidized products (Semeniuc et al., 2009).
There was no significant difference between the samples during storage (p > 0.05).Peroxide value was between 2.54-3.61meqD 2 /kg fat in control samples without addition of powder.

Viscosity
Viscosity is one of the most important factors for consumers.It has to be at an acceptable level in all kinds of cream products.The mean values for viscosity of fermented cream samples are presented in Figure 3. Viscosity values increased with the amount of milk powder supplement and kept on increasing during the storage.

Diacetyl
2,3 di-butanone, also known as diacetyl, is a major required aroma compound in fermented creams.Flavour in fermented cream products is derived from diacetyl.Many consumers evaluate fermented creams without diacetyl as flavorless (Clark et al., 2009).The mean values of diacetyl of fermented cream samples are presented in Table 3.The diacetyl values of all samples increased until 15 th day at storage and the highest value was determined on that day.Diacetyl value decreased after 15th day of storage period.The reason of this, is that bacteria rapidly degrade diacetyl to asetoine (acetyl methyl carbinol); a kind of odourless compound formed when citrate is broken down during fermentation process (Mistry, 2001).Diacetyl value was detected ranging from 0.5-2.0mg/kg in butter sample which manufactured from cultured cream (Spreer, 1998).It was considered that outcomes of fermented cream with powder addition are higher in diacetyl value than the average because of its high lactose content.

Sensory properties
Homogenous appereance, smooty structure and shiny surface are favorite characteristics in fermented cream products.Panelists were requested to evaluate appearance, body/texture, odor and flavor.Mean scores were used for comparison of the samples.Results of sensory analysis showed that sample A1 had the highest total sensory value (15.4/20.0)during the whole storage period followed by control sample (15.2/20.0),A2 (15.0/20.0),B1 (14.1/20.0),C2 (13.7/20.0),B2 (13.2/20.0)and C1 (12.8/20.0)samples, respectively.The lowest value was determined in the last day of storage (29 th day) and panelists pointed out that the products were not acceptable for consuming.Therefore, the shelf life of fermented cream with 18% fat ratio could be notified as 22 days or less.At the same time highest points of sensory analysis of all samples were detected on 15 th day of storage.These results were similar to the outputs of diacetyl values.

Conclusions
Addition of milk based powders during production of fermented cream improves the properties of the product.The higher solid and ash contents of fermented cream increase the nutritional value.Due to the high lactose content, skim milk powder, 50% and 70% demineralized whey powder enhanced activity of starter culture.Development of acidity was stimulated and the diacetyl amount which is the most important aroma compound of the fermented cream, also increased.