فصلنامه پژوهش های صنایع غذایی
سال بیست و یکم شماره 2 (زمستان 1391)

In this research، polyvinyl alcohol (PVA) and cellulose nanocrystal (NCC) were used for improving the different properties of the starch films. Cellulose nanocrystal samples prepared from cotton lint and were investigated with transmission electron microscopy (TEM). The morphological and roughness properties of the films based on starch were studied with atomic force microscopy (AFM). The results showed that adding PVA and NCC to starch based film increased and decreased roughness، respectively. The moisture absorption and contact angle analysis showed that the adding of these materials decrease the hydrophilicity of starch based films; the moisture absorption decreased from 86. 27% for plasticized starch (PS) film to 69. 73% for starch-PVA biocomposite and 54. 81% for starch-PVA-NCC (20%) bionanocomposite. The contact angle analysis showed that starch film had small contact angle after 60 second (24. 06o) and adding PVA and NCC increased contact angle to 31. 17o and 47. 71o for starch-PVA biocomposite and starch-PVA-NCC 20% bionanocomposite، respectively. The colorimetry showed that PVA didn’t affect hunter parameter but NCC increased the transparency and yellowness of starch-PVA films.

In this research، effect of sucrose replacements with sorbitol، maltitol، erythritol، xylitol and aspartame was studied. Physical properties of cake batter such as consistency and specific gravity and cake characteristics such as volume، apparent density، solid density، porosity، symmetry and uniformity، moisture and water activity، crust and crumb color and textural firmness were evaluated. Results showed that sorbitol، erythritol and aspartame caused an increase in specific gravity of batter، while xylitol and maltitol showed a significant decrease in batter specific gravity (P<0. 05). Only sorbitol replaced sample showed lower batter viscosity than that of control. Sucrose replacement with studied polyols and aspartame gave less volume، porosity and solid density and more apparent density (P<0. 05) compared to those of control sample. Samples prepared with erythritol were less uniform than control and other samples showed significant increase in cake uniformity (P<0. 05). At the first day of texture evaluation، cakes containing sorbitol، xylitol and maltitol were as firm as control sample. The hardest texture was observed in the cakes containing erythritol. In the 7th and 14th day of evaluation، samples with sorbitol and xylitol had similar firmness to that of control cakes. However، samples produced with erythritol showed the hardest texture. Cakes containing polyols and aspartame had darker crumb than that of control، while cakes prepared with sorbitol and erythritol were paler than control cakes.

Human breast milk is known to be the best food for rapidly growing infant scince breastfeeding protects the newborn against some diesease such as infection disease،asthma and allergy. This effect may be due to the useful and natural microflora of breast milk which could be depending on diets of mothers. For the first time، this study accomplished to evaluate microflora of mother’s breast milk along with sepration and identification of local bacteria that could be as a candidat for bacteriotherapy and possessing probiotic propertiesin Iran. In this study،309 different colonies were isolated from 20 breast milk samplesof mothers who were registered in Mshhad. The isolated were selected based on the results of catalase test، gram stain، and bacterial morphology. The results showed that 40 out of 309 selected bacteria were catalase negative and gram positive stain. The whole genomes of 16s ribosomal DNA of isolated colonies were amplified using polymerase chain reaction for identification down to the strain level. According to the results، the breast milk contains various species of enterococci، Streptococci، Staphylococci and Lactobacilli. The most abundant bacteria، enterococcus faeciumwasisolated from 50% of samples representing 47. 5% of the total isolated bacteria. Generally 10 and 27. 5 percentage of isolated bacteria were La. rhamnosusLc 705and Streptococcus salivarius، respectively، that were isolated from 20 and 35 percent of milk samples،respectively.

Doogh is a dairy drink which has attracted attention compared to the common drinks in use. By the application of dietary fibers، Doogh''s nutritional value will increase and the daily fiber intake requirements can be provided. The aim of the present study was to produce a stable and fiber-enriched Doogh by using gellan gum and a wheat fiber. Pasteurized and non-pasteurized Doogh samples containing gellan (0. 03% w/w) and fiber (0. 4 and 0. 8% w/w) were made and then stored at 4°C. Rheological properties، particle size distribution، phase separation and sensory attributes of the samples were analyzed. Pasteurized Dooghs containing fiber and gellan had higher shear stresses and viscosities in a constant shear rate compared to the non-pasteurized samples. The rheological properties changed from the Newtonian fluid in the control samples (without fiber and gellan) to the shear-thinning liquid (pseudo-plastic) fluid in the samples with fiber and gellan. The flow behavior index for pasteurized and non-pasteurized control samples was near one، while for the samples containing fiber and gellan (pasteurized and non-pasteurized) was less than one. Pasteurization of the samples containing fiber and gellan، in a constant fiber concentration، increased the consistency coefficient، apparent viscosity and yield stress and decreased the flow behavior index. The application of the fiber and gellan increased particle size of the samples. Moreover، the samples containing fiber and gellan were stable during storage; however، about 55% phase separation occurred in the control samples. By taking the quality indexes into account، the results showed that the best sample was the pasteurized Doogh containing gellan and fiber with the concentration of 0. 4%.

Some hydrocolloids are capable of improving the quality of bread and retarding staling. With the aim of improving the quality and delaying the staling of pan bread pectin and cross-linked pectin were added at 0، 0. 5، 0. 75 and 1% (w/w، flour basis) to the bread recipe and effected of these components on the properties of dough and bread were studied. The results showed that addition of pectin and cross-linked pectin had positive effects on water absorption of the flour. Determination of the farinograph parameters of the dough showed that addition of these components could decrease the dough arrival time، while increased the dough softening، however، other farinograph parameters remained unchanged. The control sample had the hardest texture while the sample containing 1% pectin and 0. 5% cross-linked pectin had the softest texture. The highest volume was observed for the bread containing 0. 5% pectin. Determination of the crust color showed no significant differences between breads containing either pectin or cross-linked pectin، while the control had the lightest crumb color. In general، addition of pectin and cross-linked pectin could improve the quality of bread and delay its staling. However، pectin had more positive effects on bread quality compared to the cross-linked pectin.

In this study، the composite edible films based on starch، hydroxypropylmethylcellulose (HPMC) and sunflower oil were prepared. The effect of potassium sorbate (PS) at different concentrations (2%، 6%، 10%، 14% & 18% w/w dry matter) on water vapor permeability (WVP)، ultimate tensile strength (TS) and strain at break (E%) were studied. In addition، we also investigated the ability of applied coating to retard baguette bread staling by evaluating mechanical and organoleptic properties. The PS increased WVP significantly only in high concentrations. Increasing PS concentration، E% increased from 2. 6 to 65. 7%، but TS of film significantly decreased from 7. 88 to 2. 45 Mpa. Moreover، mechanical and organoleptic tests of bread clearly indicated that applied coating was successful in retarding the staling of bread.

In this study the effects of acetic acid and sodium chloride solutions on accelerated ripening of Mazafati date cultivar were investigated. Mazafatti dates at the Khalal stage were immersed in acetic acid solution (0. 5، 1. 5 and 2. 5%) and NaCl (1، 2 and 3%) solution for 5 minutes and then incubated at 39±1 C for 80 hrs. The results indicated that incubation was the main factor in accelerated ripening of Mazafati date and about 85% of the samples ripened only by incubation. Acetic acid and NaCl solutions had little effect compared to the incubation treatment and played a complimentary role on ripening of date fruit. Dry weight and total soluble solid of the samples increased، while pH and total insoluble solid in water and textural hardness decreased during ripening. Overall، the treatments discussed in this paper can be regarded as a good method for accelerated ripening of Mazafati date.

Toffee is considered a popular type of confectionary product with the high acceptability. The main components of toffee comprises of sugar، glucose syrup، and fat which are mixed at appropriate percentage in presence of water or milk and subjected to high heat treatment. In this research، the effect of permeate (obtained from UF process of milk) addition on physicochemical and textural (measured by Texture Analyzer) properties of toffee were investigated. Data from this study were statistically analyzed using «limited mixed experimental design methodology» for comparison of treatments with each other. The ingredients were used consist of glucose syrup in the range of 10-60%، sugar in the range of 10- 60%، and cheese permeate in the range of 0- 50%. The level of fat in all formula remains fixed and the control sample was prepared with milk powder and in accordance with toffee commercial formula. Moisture content، water activity، ash، texture (hardness، springiness، chewiness، gumminess، adhesiveness، and cohesiveness)، as well as color measurement and organoleptic properties (texture، color، taste، appearance and total acceptance) were assessed for all trials. The statistical analysis showed a significant differences between all trials and the control (P<0. 05). As the permeate level increased، the moisture content was decreased and the ash content was increased in all formulas and also the cohesiveness was increased (P<0. 05). The optimum level for permeate based toffee was achieved by mixing 26. 6% permeate، 36. 6% glucose syrup، and 36. 6% sugar.

Sourdough plays a key role in improving flavour, texture, nutritional and shelf-life of bakery products. Studies have shown that the microorganisms of sourdough influence the properties of final product. Therefore, selected lactic acid bacteria which are the dominant microflora of sourdoughs were used. In this study L. plantarum, L. reuteri and a mixture of both bacteria were used in the preparation of freeze-dried sourdoughs. Results showed that L. reuteri led to a slight decrease in pH of sourdough. Survival rate of L. reuteri was higher than that of L. plantarum. Thus, L. reuteri resisted in freeze drying process and can be regarded as a suitable candidate for production of type-III sourdough.

In this research، response surface methodology was used to investigate the influence of Barbari bread improver gel components on the dough stickiness and optimization of gel formulation. Gel samples were prepared using sodium stearoyl-2-lactylate (SSL)، diacetyl tartaric acid esters of monoglyceride (DATEM) and propylene glycol (PG) in the range of 0-0. 5 g/100g. Results showed that addition of all three components to the gel formula caused decrement in the stickiness force. Although stickiness distance increased by addition of the components، but it was significantly decreased by SSL square and interaction of DATEM and PG. Stickiness area just affected by SSL square and other parameters did not have any significant effect on it. The represented models have high determination coefficients and could be used for prediction of all investigated characteristics. The results for optimization using central composite design suggested that a mixture containing 0. 5 g/100g of SSL، 0. 5 g/100g of DATEM and 0. 5 g/100g of PG could be a good improver gel to achieve the minimum stickiness.