جستجوی مقالات مرتبط با کلیدواژه « Lactose » در نشریات گروه « کشاورزی »

Among the foods consumed on a daily basis, milk has the most appropriate and balanced ingredients, that is the reason milk called whole food. Milk is the only known substance in nature that can provide the human body with complete and balanced nutrition. Recombined milk is a milk replacement product. Recombined milk components are more easily adjustable than milk components. The electrical conductivity is referred to as conductivity of specific material against the electric current, which is expressed in micro Siemens units per cm (mS/cm). Using electrical conductivity, valuable information is available about the quality of different materials, including food. In addition, by this method, as a simple and practical tool, the quality of many foods can be controlled. The aim of this study was to investigate the electrical conductivity of recombined milk affected by temperature, protein percentage, and lactose content.

In order to investigate the effect of protein percentage (1, 2 and 3%) and percentage of lactose or sugar content (4, 6 and 8%) on the electrical conductivity of milk, pure dry milk powder without dietary supplementation was used. Lactose powder was used to increase the lactose content of dry milk powder. Sodium caseinate was used to increase the protein content of dry milk powder. Distilled water was used to increase the volume of samples. Total experiments were carried out at three temperature levels (50, 55 and 60 ºC). Data analysis was also done using SPSS 16 software.

The results showed that temperature, protein percentage, and lactose percentage had a significant effect on the electrical conductivity of recombined milk. The electrical conductivity of the recombined milk ranged from 2.31 to 5.7 mS/cm at 50°C, 8% lactose, 1% protein, and 60°C, 4% lactose, 3% protein, respectively. The greatest and least effect on the electrical conductivity of recombined milk was related to the effect of protein percentage and lactose percentage, respectively. By increasing the temperature, the electrical conductivity of the reconstituted milk has increased significantly. The greatest changes in electrical conductivity (16%) of recombined milk occurred by the influence of temperature factor in protein 1% and lactose 4% and its value ranged from 2.44 to 2.83 mS/cm. In addition, the lowest changes in electrical conductivity (6%) of recombined milk were obtained by the temperature factor of 3% protein and 8% lactose, and it was increased from 4.68 to 4.95 mS/cm. By increasing protein content, the electrical conductivity of recombined milk has increased significantly. The most changes in electrical conductivity (107%) of recombined milk occurred by the influence of protein percentage at 55 °C and 6% lactose and its value ranged from 2.42 to 5.6 mS/cm. In addition, the lowest changes in the electrical conductivity (100%) of reconstituted milk occurred by the influence of protein percentage at 55 °C and 4% lactose, and its content increased from 2.5 to 5 mS/cm 5. These results indicate that the protein percentage factor has the most effect on the electrical conductivity of recombined milk (compared to two temperature factors and lactose percentage). By increasing lactose content, the electrical conductivity of recombined milk has decreased significantly. The greatest changes in electrical conductivity (13%) of recombined milk occurred by the influence of lactose percentage at 60 °C and protein 3% and its content decreased from 5.7 to 4.95 mS/cm. Also, the smallest changes in electrical conductivity (1.5%) of reconstituted milk occurred by the influence of lactose percentage at 55 °C and 2% protein, and its content decreased from 5.55 to 4.48 mS/cm. The maximum and minimum amount of electrical conductivity of reconstituted milk was 5.7 mS/cm at 60°C, 4% lactose and 3% protein, and 2.31 mS/cm at 50°C, 8% lactose and 1% protein, respectively.

Doogh is one of the most important and most widely consuming fermented traditional Iranian milk products, which is being prepared from the healthy milk by using the activity of certain lactic acid bacteria and molds under the especial conditions. Streptococcus thermophilus and Lactobacillus bulgaricus are used as starter culture for milk fermentation. The fermented dairy products have long storage life and constitute an important part of the milk's per capita consumption. For this reason, studying the different methods in order to improve the quality of these products is crucial. By considering the fact that the strong thermal treatments damage some components of milk such as protein and vitamins, using the membrane filterations decrease the need to impose the intense thermal conditions which result into the relative loss of nutrients. On the other hand, using the membrane filters not only increase SNF (solid non-fat) and the percentage of protein but also lead into the production of less-lactose milk as well, the production of less-lactose products, in addition to their nutritional value for some people, have especial benefits for improving the quality. As follows, UF filters in 10-2-10-1 diameter separate the bacteria, fats and protein when milk is passing with a pressure about 1-10 bar but also they pass the minerals such as salts and water which are being removed as permeate and the concentrated milk is called “Retentate”.

Materials provided in this study were including: Starter culture (No: 505 form Danisco, USA), Lactic acid (1.00366) with a degree of purity level more than 95%, NaH2PO4*2H2O (1.06345) plus the cultures' environment and the chemical substances from MERCK Company. HPLC system (Agilent, 1100 series, USA), Rheometer (Anton, MCR300, Austria), Milk analyzer bar (Azmalaban, MCC, Iran), pH meter (Knick,766, Germany), Digital scale 0.001 (AND,GF4000, Japan), Psychrometer (Sartorius, MA45, Germany), Oven (memmert, UM400, Germany), Centrifuge (Funke Gerber, Nova safety, Germany), Kjeldahl (Gerhardt, KB, Germany), Refrigerated incubator (WTW,TS606-6/2-i, Austria), Incubator (memmert, BM400, Germany),  Autoclave (RT-2, Reyhan Teb, Iran). In the present study the effect of a decrease in lactose percentage on the durability, flavor and sensory (organoleptic) properties of produced doogh on the 1st, 23rd and 46th day’s after production time in comparison to control ones, was  investigated. The changes of acetaldehyde levels were measured using Gas chromatography mass spectroscopy. In this study, milk was passed through UF filters in three consecutive days and its lactose level was decreased by about 2%. After that fermentation and standardization of doogh based on the amount of fat and solid-nonfat has been done. All tests were repeated 3 times and the comparison of averages has been done by using LSD test (p= 0.05 %). Results were expressed as mean ± SE. Values were the average of triplicate experiments. Significant differences between the results were calculated by analysis of variance (ANOVA) with the help of SPSS software version 20. Differences at P<0.05 were considered to be significant. Also the obtained data for the rheological experiments was processed using software such as Excel 2010 and SPSS software version 20 to determine an appropriate mathematical model. And in this case, the linear and nonlinear regressions were used.

Results showed that by increasing the storage time, the acidity and pH changes and the acetaldehyde amount of produced doogh was less than those of the control samples. Additionally flavor and sensory properties improved considerably. Based on the findings of this research, it seems that the reduction of lactose and the decrease of lactic acid bacterial activity can play an important role in increasing the durability time, improving the sensory properties and enhancing the quality of doogh. It was determined that the decrease of lactose using ultrafiltration to the control sample not only indicates the significant changes in most considered variables but also there are these kinds of changes during the durability time. In addition, the significant and slow changes of pH to the control sample due to the decrease of lactic bacteria activities show the least qualitative and flavor changes over the durability time. And also it was specified that by increasing the activities of lactic bacteria, the amount of acetaldehyde will increase but by decreasing this activity, the level of acetaldehyde will decline. This issue has a direct relationship with the changes of lactose's amount. The post-filtration doogh due to its high amount of proteins shows high viscosity and concentration and for this reason, the attention of panelists in the sensory evaluation was directed toward choosing the post-filtration doogh instead of the pre-filtration one. Therefore, it can be concluded that the decrease of lactose using ultrafiltration has a main role in improving the quality of the product and also the tendency of the consumers.