EFFECT OF HIGH HYDROSTATIC PRESSURE PROCESSING ON RHEOLOGICAL AND TEXTURAL PROPERTIES OF PROBIOTIC LOW-FAT YOGURT FERMENTED BY DIFFERENT STARTER CULTURES

The effect of milk processing on rheological and textural properties of probiotic low‐fat yogurt (fermented by two different starter cultures) was studied. Skim milk fortified with skim milk powder was subjected to three treatments: (1) thermal treatment at 85C for 30 min; (2) high hydrostatic pressure (HHP) at 676 MPa for 5 min; and (3) combined treatments of HHP (676 MPa for 5 min) and heat (85C for 30 min). The processed milk was fermented using two different starter cultures containing Streptococcus thermophilus, Lactobacillus delbrueckii ssp. bulgaricus, Lactobacillus acidophilus and Bifidobacterium longum at inoculation rates of 0.1 and 0.2%. Rheological parameters were determined and a texture profile analysis was carried out. Yogurts presented different rheological behaviors according to the treatment used, which could be attributed to structural phenomena. The combined HHP and heat treatment of milks resulted in yogurt gels with higher consistency index values than gels obtained from thermally treated milk. The type of starter culture and inoculation rate, providing different fermentation pathways, also affected the consistency index and textural properties significantly. The combined HHP and heat treatment of milks before fermentation, and an inoculation rate of 0.1% (for both cultures), led to desirable rheological and textural properties in yogurt, which presented a creamy and thick consistency that does not require the addition of stabilizers.     

ASSESSMENT OF POTENTIAL PROBIOTIC PROPERTIES OF LACTIC ACID BACTERIA AND YEAST STRAINS

ABSTRACT

Four lactic acid bacteria (LAB) and three yeast strains isolated from a traditional Bulgarian cereal-based fermented beverage were assessed for potential probiotic properties. Acid and bile resistance, antipathogenic activity and antibiotic resistance of the strains were evaluated. Tolerance to low pH values (2.0–3.0) and high bile concentrations (0.2–2.0%) of the LAB and yeast strains varied, but all strains kept viable throughout the experiments. Antagonistic activity towards most of the eight test-pathogens was observed for one LAB (Lactobacillus plantarum B28) and two yeast strains (Candida rugosa Y28 and Candida lambica Y30). Antibiotic resistance (39 antibiotics) of the LAB strains was variable, but showed their potential for therapeutic application.     

ASSESSMENT OF POTENTIAL PROBIOTIC PROPERTIES OF LACTIC ACID BACTERIA AND YEAST STRAINS

Four lactic acid bacteria (LAB) and three yeast strains isolated from a traditional Bulgarian cereal-based fermented beverage were assessed for potential probiotic properties. Acid and bile resistance, antipathogenic activity and antibiotic resistance of the strains were evaluated. Tolerance to low pH values (2.0-3.0) and high bile concentrations (0.2-2.0%) of the LAB and yeast strains varied, but all strains kept viable throughout the experiments. Antagonistic activity towards most of the eight test-pathogens was observed for one LAB (Lactobacillus plantarum B28) and two yeast strains (Candida rugosa Y28 and Candida lambica Y30). Antibiotic resistance (39 antibiotics) of the LAB strains was variable, but showed their potential for therapeutic application.     

EFFECT OF TYPE AND LEVEL OF STARTER CULTURE ON THE RHEOLOGICAL PROPERTIES OF SET YOGURT DURING GELATION PROCESS

The effect of type and level (2, 3, 5%) of starter cultures on the rheological properties of set yogurt during gelation process was studied using a cylindrical rotational viscometer. At the beginning of the gelation process the viscosity was constant after which the viscosity rose rapidly and reached a maximum value and then gradually decreased. The results indicate that the starter type and level have a definite effect on yogurt viscosity during gelation process. The Ostwald-de Waele power-law model was used to characterize the flow behavior of the curd.     

RHEOLOGICAL PROPERTIES OF OIL-IN-WATER EMULSIONS FORMED WITH MILK PROTEIN CONCENTRATE

The rheology and the microstructure of emulsions stabilized with milk protein concentrate (MPC) were investigated using different MPC and oil concentrations. Steady‐shear tests showed that the emulsions were Newtonian at low oil concentrations (<20 wt%), whereas they were pseudoplastic and thixotropic at high oil concentrations (>20 wt%). Dynamic rheological measurements demonstrated that these emulsions behaved as weak gels, as indicated by relatively high values of G′ to G″. The rheological behavior of these emulsions was consistent with bridging flocculation mechanisms, whereby more than one droplet is shared by adsorbed casein aggregates/micelles. This was confirmed by confocal microscopy, which showed that these emulsions were aggregated.     

多菌种混合乳酸菌发酵酸豆奶工艺研制

本文研究了市售酸牛奶和自制酸泡菜中分离筛选菌种，确定菌种间的比例。通过对生产过程中的条件进行初步摸索，以鲜豆奶为主要原料，采用多菌种混合液态发酵，可生产出色、香、味俱佳，不舍任何防腐剂的纯天然酸豆奶新产品，从而为工业化生产乳酸菌发酵酸豆奶提供技术依据。     

RHEOLOGICAL AND PHYSICOCHEMICAL BEHAVIOR OF FORTIFIED YOGURT, WITH FIBER AND CALCIUM

Yogurt systems were prepared from whole milk, adding 50 mg of calcium/100 mL of yogurt, and three levels of fiber from two wheat‐bran sources. In comparison with a plain yogurt, the presence of fiber and calcium augmented the consistency, diminished the syneresis and the pH was higher. Fiber increased the consistency, and all the formulated samples exhibited a non‐Newtonian response. During 3 weeks of storage time, the consistency reduced (from 2.0 to 0.32 Pa·s ⁿ ), syneresis increased (from 20 to 48%) and pH decreased (from 4.5 to 4.2) as a function of the system formulation.     

EFFECT OF MINERAL FORTIFICATION ON RHEOLOGICAL PROPERTIES OF WHOLE WHEAT FLOUR

This study was aimed to evaluate the rheological changes that take place in the dough as a result of addition of elemental iron, ferric sodium ethylenediaminetetraacetate, zinc sulphate and zinc oxide in various combinations to whole wheat flour (WWF), packaged in polypropylene woven bags and tin boxes and stored for a period of 60 days under ambient and controlled conditions of temperature and relative humidity. Water absorption (WA) capacity, dough development time (DDT) and dough stability time (DS) of the fortified WWF were measured by farinographic method, and peak viscosity was assessed by viscographic analyses. WA capacity and DDT of flours increased during storage. Fortification significantly (P  <  0.05) affected WA, DDT, DS and viscographic characteristics of the flours. Packaging materials (P  <  0.05) influenced WA, DDT and DS, while storage condition had only affected viscographic properties of the flours.

PRACTICAL APPLICATIONS

The success of any fortification program depends on the stability of micronutrients and food to which they are added. Exposure of the fortificants to any of the physical and chemical factors including heat, moisture, air, or light and acid or alkaline environments during food processing, packaging, distribution or storage affects their stability. The rheological properties of dough made from fortified flours determine the quality of the fortified end product. Changes in rheological properties as a result of the incorporation of fortificants in the flour, its storage under variable conditions and length of time might have an effect on quality, cost and nutrition of the product.     

干酪质地及流变学特性的研究进展

介绍了有关干酪的成分及工艺过程对质地和流变学特性影响的研究。在干酪成分中，蛋白质是影响产品流变学特性的主要因素，酪蛋白空间形成的网状结构构成了干酪流变学的基础。在加工过程中，pH、温度、钙浓度、蛋白水解等所有对干酪成分分子产生变化的因素都可能使干酪的流变学特性和质地发生变化。因此，干酪流变学特性的研究对更好地控制质地，生产出质优价廉的干酪，具有重要的意义。最后，研究状况进行了展望。     

INFLUENCE OF CARRAGEENAN AND TOTAL SOLIDS CONTENT ON THE RHEOLOGICAL PROPERTIES OF LACTIC BEVERAGE MADE WITH YOGURT AND WHEY

The purpose of this work was to study the influence of carrageenan level (X₁) and total solids content of yogurt/whey mixture (X₂) on starter culture fermentation time, physicochemical properties (pH, fat and total solids contents) and rheological characteristics of lactic beverages using response surface methodology. The physicochemical characteristics of the lactic beverages were similar to those of commercial products. All beverages showed non-Newtonian fluid behavior with thixotropy and yield stress. The total solids content of the lactic beverages had a greater influence on the rheological behavior of these products than the carrageenan level. Wide ranges of consistency measurements were observed by varying the stabilizer level and total solids content.     

EFFECTS OF INULIN AND BULKING AGENTS ON SOME PHYSICOCHEMICAL, TEXTURAL AND SENSORY PROPERTIES OF MILK CHOCOLATE

Chocolates are favorite foodstuffs with high sugar contents. Therefore, in the present study, the production of a low-sugar milk chocolate with prebiotic properties is evaluated. Various ratios of inulin (IN), polydextrose (PD) and maltodextrin (MD) along with sucralose (0.04% w/w) were used instead of sugar. Fifteen formulations were examined to determine some physicochemical, mechanical and sensory properties in order to find their optimum ratios. In general, formulations with high ratios of PD and MD were moister and softer than control. The lowest moisture content and highest hardness were observed for the moderate ratios. In addition, MD induced the least desirable sensorial effects, whereas PD and IN pronouncedly improved the overall acceptability. The optimum applicable range for IN, PD and MD were 14–32% and 71–84%, 7–26% and 67–77%, and 0–20% of sugar substitutes, respectively. Our findings on simultaneous fat and sugar reductions also indicated the possibility of fat cut up to 5% in comparison to previous fat content.

PRACTICAL APPLICATIONS

In this paper, we have reported the influences of inulin (IN) as a prebiotic as well as polydextrose (PD) and maltodextrin (MD) as bulking agents on physicochemical, energy content, texture and sensory properties of milk chocolate using simplex lattice mixture design. To the best of our knowledge, this is the first report in this field with very interesting results and practical applicability. Moreover, our findings showed that the use of aforementioned ingredients instead of sugar could lead to production of low-calorie milk chocolate without having the undesirable textural and physiological effects on the product and consumers. Moreover, the simplex lattice mixture design was found a very useful technique for finding optimum ratios of sugar replacers in formulation.