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。     

EFFECT OF ADDITIVES ON RHEOLOGICAL CHARACTERISTICS AND QUALITY OF WHEAT FLOUR PAROTTA

Effects of oxidizing agents (potassium bromate [20 and 40 ppm], ascorbic acid [100 and 200 ppm] and potassium iodate [20 and 40 ppm]), reducing agents (potassium metabisulphite [100 and 200 ppm] and cysteine hydrochloride [50 and 100 ppm]), enzymes (fungalα‐amylase [10 and 20 ppm] and protease [10 and 20 ppm]) and dry gluten powder (1, 2 and 3%) on rheological characteristics of dough and quality of parotta were studied. Addition of oxidizing agents and dry glutenincreased values for farinograph stability, extensograph and mixograph areas, apparent biaxial extensional viscosity, compressive stress, hardness and cohesiveness, while reducing agents and enzymes decreased the aforementioned characteristics and increased force decay parameter and adhesiveness of the dough. Among the different additives studied, incorporation of 100‐ppm potassium metabisulphite, 50‐ppm cysteine hydrochloride and 10‐ppm protease increased the overall quality score of parotta.     

The Effect of Low-Temperature Storage on the Glycoalkaloid Content of Potato (Solanum tuberosum) Tubers

Tubers from six cultivars selected on the basis of their rates of glycoalkaloid accumulation in response to light exposure were stored at 10, 7 and 4°C. After 9 weeks at 10°C a subset from each cultivar was removed and subsequently stored at lower temperatures. Samples were removed after 9, 18 and 24 weeks storage and analysed for their glycoalkaloid content. At all temperatures the rate of glycoalkaloid accumulation was independent of the level found at harvest and significant interactions were found between cultivar and temperature. The highest rates of accumulation were seen in tubers from the cultivars Brodick and Pentland Crown stored at 4°C. During the first 9 weeks of storage at this temperature the glycoalkaloid content of these two cultivars increased by 7·4 and 19·1 mg per 100 g fresh weight respectively and thereafter remained constant. At 7°C glycoalkaloid content tended to increase more rapidly than at 10°C with again the greatest increases being found for Brodick and Pentland Crown. In the case of the former glycoalkaloid content increased linearly during the 24 weeks of the experiment but the glycoalkaloid content of Pentland Crown tubers stored at 7°C increased rapidly in the first 9 weeks and thereafter increased more slowly, reaching a final value which exceeded the recommended maximum glycoalkaloid concentration for human consumption by 50%. Cultivars which did not accumulate glycoalkaloids rapidly in response to light exposure were the most stable and least sensitive to storage temperature. Tubers transferred to colder conditions nine weeks after storage at 10°C did not accumulate glycoalkaloids at a similar rate to those placed in similar conditions soon after harvest. © 1997 SCI     

Microstructural,cooking and textural characteristics of potato (Solanum tuberosum L) tubers in relation to physicochemical and functional properties of their flours

Potato tubers from six different cultivars were freeze‐dried, ground into flour and analyzed for thermal, pasting and textural characteristics (using differential scanning calorimetry, Rapid Visco analyzer and Instron universal testing machine, respectively) to study the relationship between flour characteristics and cooked potato mealiness. The potatoes with higher sensory mealiness scores resulted in flours having lower transition and pasting temperatures, higher amylose content, setback, peak and final viscosity. The flour gels from the mealier potatoes also exhibited higher values of textural parameters such as hardness, cohesiveness, chewiness and springiness. The microstructure of the tuber parenchyma (studied using scanning electron microscopy), cooking and sensory characteristics of potatoes were found to be related to the pasting and textural characteristics of their flours. Potato cultivars with lower mealiness scores, loosely packed cell arrangement, with comparatively large‐size cells and thinner cell walls showed lower values of textural parameters for both raw and cooked potatoes. This information may prove useful for the selection of potato cultivars with desirable textural and flour‐making properties for specific end‐uses. Copyright © 2005 Society of Chemical Industry     

Textural and pasting properties of potatoes (Solanum tuberosum L.) as affected by storage temperature

Fresh tubers from five potato (Solanum tuberosum L.) cultivars were stored at different temperatures (4, 8, 12, 16 and 20 °C) and 80–90% relative humidity for 18 weeks after harvest to examine the effect of storage temperature on their textural and pasting properties. Texture profile analysis was performed on raw and cooked potatoes using an Instron universal testing machine to measure textural parameters such as fracturability, hardness, cohesiveness, adhesiveness and springiness. Both raw and cooked potato tubers showed a considerable reduction in all textural parameters upon storage, irrespective of the storage temperature employed. Raw potatoes showed a decrease in fracturability and hardness with increasing storage temperature, whereas their cooked counterparts showed the opposite trend. The extent of change in the textural properties of both raw and cooked potatoes also varied among the different cultivars. Fresh and stored tubers from all cultivars were freeze‐dried, ground into flours and analysed for amylose content and pasting properties. The amylose content of flours prepared from potatoes stored at 4 and 8 °C was observed to be considerably lower than that of flours prepared from potatoes stored at 16 and 20 °C. Pasting characteristics such as peak viscosity, setback and final viscosity increased with increasing storage temperature, while the reverse was observed for pasting temperature, when studied using a rapid visco analyser. Breakdown in viscosity of the flour pastes from all cultivars was considerably reduced during storage, irrespective of the storage temperature employed. Copyright © 2006 Society of Chemical Industry     

EFFECT OF THE AMOUNT AND PARTICLE SIZE OF WHEAT FIBER ON TEXTURAL AND RHEOLOGICAL PROPERTIES OF RAW,DRIED AND COOKED NOODLES

ABSTRACT

Textural and rheological properties of raw, dried and cooked noodles enriched with wheat fibers were simultaneously evaluated by a texture analyzer. Increasing wheat fiber level led to an increase in the cutting force of raw and cooked noodles and a decrease in the breaking force of dried noodle as well as extensibility of raw and cooked noodles. Generally, raw, dried and cooked fiber‐enriched noodles with small fiber size had higher breaking force and extensibility and lower cutting force than that with large fiber size. The textural properties of raw noodle are good indicators to predict the strength and elasticity of dried and cooked noodles. Both three‐term Maxwell and Peleg–Normand models were found to fit well to the stress relaxation data of cooked fiber‐enriched noodle. Significant correlations were found between empirical textural properties and fundamental mechanical stress relaxation parameters.

PRACTICAL APPLICATIONS

Texture is one of the important factors affecting the quality of noodles. The increased consumption of noodles enriched with wheat bran or purified wheat fiber is proposed for health reasons. The textural properties of fiber‐enriched noodles are affected by the type, amount and size of wheat fiber. The cutting force, tensile strength and extensibility of raw noodle are good indicators to predict the strength and elasticity of dried and cooked noodles. Results of this study suggest that raw, dried and cooked fiber‐enriched noodles with good quality can be prepared by adding 4–8% fine wheat bran or 4% fine purified wheat fiber.     

Photo-induced changes in the total chlorogenic acid content of potato (Solanum tuberosum) Tubers

The exposure of potato tubers to light resulted in a significant cultivar-dependent increase in chlorogenic acid content. The magnitude of the observed increase resulting from 48 h light exposure was significantly correlated with the initial chlorogenic acid content of the tubers and also with the previously reported photo-induced increases in total glycoalkaloids. Time-course studies indicated that the greatest rate of increase occurred between 8 and 16 h continual exposure. Prolonged storage under light revealed that chlorogenic acid values in some cultivars reached a maximum value after 48 h, whilst in others these continued to increase almost linearly until the end of the experiment 5 days later.     

EFFECT OF COLD STORAGE ON CULTURE VIABILITY AND SOME RHEOLOGICAL PROPERTIES OF FERMENTED MILK PREPARED WITH YOGURT AND PROBIOTIC BACTERIA

ABSTRACT

We examined the effect of storage time on culture viability and some rheological properties (yield stress, storage modulus, loss modulus, linear viscoelastic region, structural recuperation and firmness) of fermented milk made with Lactobacillus delbrueckii ssp. bulgaricus, Lactobacillus acidophilus (LA) and Bifidobacterium animalis ssp. lactis in coculture with Streptococcus thermophilus (ST). Acidification profiles and factors that affect viability (postfermentation acidification, acidity and dissolved oxygen) were also studied during 35 days at 4C. Fermented milk prepared with a coculture of ST and Bifidobacterium lactis gave the most constant rheological behavior and the best cell viability during cold storage; it was superior to ST plus LA for probiotic fermented milk production.

PRACTICAL APPLICATIONS

Probiotic cultures should grow quickly in milk, provide adequate sensory and rheological properties to the product, and remain viable during storage. Commercially, it is very common to use yogurt starter culture (i.e. Streptococcus thermophilus[ST] and Lactobacillus delbrueckii ssp. bulgaricus) in combination with the probiotic bacteria in order to reduce fermentation time. However, LB tends to post acidify fermented milk, which reduces the viability of the probiotic bacteria; thus, it is recommended to use starter cultures devoid of this species. We found that the technological properties and the viability of the probiotic bacterium Bifidobacterium animalis ssp. lactis BL O4 in coculture with ST make it suitable for probiotic fermented milk production; it produces rheological characteristics similar to those of yogurt.     

The effect of prior storage on the potential of potato tubers (Solanum tuberosum L) to accumulate glycoalkaloids and chlorophylls during light exposure,including artificial neural network modelling

Potato tubers of four varieties (Brodick, King Edward, Pentland Dell and Record) were stored under commercial conditions and exposed to light for up to 10 days after 0, 10, 20 and 30 weeks. These were analysed for photosynthetic pigment and glycoalkaloid content. There was no significant alteration in either tuber chlorophyll or glycoalkaloid content during dark storage. All four varieties greened in response to light exposure, but only three exhibited a significant increase in glycoalkaloid concentrations during this exposure. Storage duration did not significantly affect pigment accumulation. However, there was a marked effect of storage on the extent of glycoalkaloid accumulation. Tubers of all four varieties stored for more than 10 weeks did not accumulate glycoalkaloids to the same extent as fresh tubers. Indeed, Brodick and Record did not accumulate any glycoalkaloids in response to light after 30 weeks of storage. A number of artificial neural network models of the results were produced. These accurately modelled cultivars individually, but a model encompassing all the data was not successful at predicting cultivar differences. © 1999 Society of Chemical Industry     

A Method for Intercultivar Comparison of Potato Tuber Nutrient Content Using Specific Tissue Weight Proportions

ABSTRACT:  Potato tubers are a staple food item in the North American diet. Each potato cultivar has unique tuber appearance and nutritional composition. A method was developed to facilitate better cultivar selection for dietary purposes and obtain a better understanding of the nutrient distribution within specific tissues of potato tubers. This involved a procedure for estimating the percent weight contribution of the 3 major tissue components, including periderm or "skin," cortex, and pith for 20 potato cultivars. Weight determination was based on the volume (calculated through an ellipsoid formula) and density of each component tissue. Calculated percent weight and dry matter data for each tuber tissue provided conversion factor values that were tabulated for all cultivars. An example is provided to illustrate the application of this procedure in facilitating identification of cultivars with significantly greater or lesser protein content.