پیش‌بینی و بهینه‌سازی پارامترهای رئولوژیکی نشاسته سیب‌زمینی اصلاح شده با پلاسمای سرد

در این تحقیق نشاسته سیب‌زمینی توسط پلاسمای سرد تیمار و سپس در دماهای مختلف خشک شد. پلاسمای سرد با استفاده از یک راکتور پلاسما شامل الکترودهای مسی و فولادی، ولتاژ kv 20، با جریان ma 3 دارای hz 50، با کمک هوای اتمسفر تولید و با نمونه برخورد ‌کرد. سپس رفتار جریان دیسپرسیون 2 درصد نشاسته با مدلهای رئولوژیکی قانون توان، هرشل- بالکلی و کسون با کمک جعبه ابزار نرم رگرسیون نرم‌افزار spss 20 برازش شدند. نتایج نشان دادند مدل هرشکل-بالکلی توانسته است در بیشتر موارد برازش دقیق‌تری با داده‌ها داشته باشد. با افزایش دمای پیش ژلاتینه شدن، ویسکوزیته نهایی نمونه‌های نشاسته کاهش یافته است. ضریب n در نمونه‌هایی که پیش ژلاتینه نشده بودند، با افزایش سایر فاکتورها افزایش یافت اما در نمونه‌هایی که در دمای ℃55 پیش تیمار شده بودند، با افزایش سایر فاکتورها کاهش نشان داد. دمای خشک کردن به طور کلی باعث کاهش ویسکوزیته نمونه‌ها شد. در هر دما، اثر دمای پیش ژلاتینه و زمان تیمار با پلاسمای سرد بر تغییرات ویسکوزیته معنادار بود. ضرایبی مانند k و n نیز با افزایش دمای خشک کردن، کاهش یافتند. افزایش زمان تیمار با پلاسمای باعث کاهش ویسکوزیته و k در نمونه‌ها شد. اما نوسانات قابل توجهی در مقدار n از خود نشان داد. در نمونه‌هایی که بیشترین زمان تیمار با پلاسمای سرد یعنی 30 دقیقه را دریافت کرده بودند، افزایش دمای خشک کردن و دمای پری ژلاتینه کردن باعث کاهش n و تغییر رفتار سیال از حدود نیوتنی، به رقیق شونده با برش شد. نتایج این پژوهش نشان دهنده اثر تیمار پلاسمای سرد بر رفتار رئولوژیکی نشاسته سیب زمینی بوده و راهکارهایی برای بهینه‌سازی فرآیندهای صنعتی مرتبط با تولید و کاربرد این نوع نشاسته را نیز فراهم کرده است.

prediction and optimization of rheological parameters of potato starch modified by cold plasma

introduction: starch is a crucial ingredient in the production of various food products, with its functional properties varying depending on the source. however, the use of natural starch in industrial applications has been met with several challenges. these include the low temperature at which starch paste forms, limited tolerance of natural starch to various processing methods, and the low hardness of the gels it forms. these factors ultimately constrain the widespread use of natural starch, particularly in the food industry. to overcome these limitations, starch modification is commonly performed after its extraction using various methods, including chemical, physical, enzymatic, and thermal processes. these modifications alter the functional properties of starch, enhancing its applicability in the food industry, depending on the specific conditions applied. plasma-active species, in particular, interact with starch through three main mechanisms: crosslinking, depolymerization, and removal of granule surfaces, which further modify its properties.materials and methods: potato starch powder was sourced from zamen food products manufacturing company, located in mashhad industrial city, iran. the starch was stored in plastic packaging, ensuring it remained sealed and free from exposure to external air. for the cold plasma treatment, a homemade cold plasma generator was used. this device consists of two main sections: the cold plasma generation unit and a sample storage compartment. it is capable of producing cold plasma and facilitating direct contact between the sample and ionized air. a plasma reactor equipped with copper and steel electrodes was used to generate a voltage of 20 kv and a current of 3 ma at 50 hz, with atmospheric air facilitating the collision of the plasma with the sample. to prepare the starch samples, a randomized complete factorial experimental design was applied, with factors including pre-gelatinization temperature (60, 55, and 0°c), cold plasma treatment time (30, 15, and 0 minutes), and starch drying temperature (80, 70, and 60°c). following this, a 2% (w/w) suspension of potato starch was heated at 100°c for 1 hour. the suspension was vortexed every 5 minutes, and after 1 hour, the samples were allowed to cool to room temperature (25°c). the shear flow behavior of the 2% starch dispersion at 25°c was measured using a viscometer (made in spain) with a no. 3 spindle. shear stress was applied incrementally over a range of 0 to 200 inverse seconds, and strain data were recorded. the fluid flow behavior of the starch dispersion was then analyzed using various rheological models. the flow data were fitted to the power law, herschel-bulkley, and casson models using the nonlinear regression tool in spss 20 software.results and discussion: the herschel-bulkley model provided the best fit for the data in most cases, although the power law and casson models also yielded good fits in certain treatments. this suggests that the type of treatment can result in a range of behaviors, from newtonian to non-newtonian thinning in the starch fluid. in general, as the pre-gelatinization temperature increased, the final viscosity of the starch samples decreased. however, for samples that were not pre-gelatinized, the coefficient k increased with plasma treatment time, rising from zero to 15 minutes. in samples that were not pre-gelatinized, the coefficient n increased with the other factors. however, in samples pretreated at 55°c, n decreased as the other factors increased. at a pre-gelatinization temperature of 60°c, the value of n remained constant but was generally lower than that of the other pre-gelatinization treatments. the drying temperature generally decreased the viscosity of the samples. nevertheless, at each drying temperature, the effects of pre-gelatinization temperature and cold plasma treatment time on viscosity changes were significant. both k and n coefficients decreased with increasing drying temperature. additionally, increasing plasma treatment time led to a decrease in viscosity and k, although significant fluctuations in the value of n were observed. for instance, in samples that did not undergo plasma treatment, pre-gelatinization and drying at the lowest temperature resulted in a newtonian to shear-thickening behavior (n=1.1) in the fluid. however, increasing the drying temperature at the same pre-gelatinization temperature caused n to decrease to around 0.83. in contrast, for samples that received 15 minutes of plasma treatment, the key factors influencing changes in n were the drying and pre-gelatinization temperatures. finally, in samples subjected to the longest cold plasma treatment time of 30 minutes, increasing both drying and pre-gelatinization temperatures led to a decrease in n, shifting the fluid behavior from newtonian to shear-thinning.conclusion: the study of the effect of cold plasma treatment on the rheological properties of potato starch reveals a significant influence of temperature and treatment time on both the viscosity behavior and molecular structure of the starch. the results highlight that cold plasma treatment, particularly at temperatures below 60°c, has a marked effect on reducing rheological parameters such as starch viscosity and consistency. these changes in rheological properties result from the chemical and physical effects of cold plasma active species on starch granules, including alterations to the granule surface, the formation of pores, and increased water absorption. additionally, it was found that starch modification through cold plasma treatment enhances its functional properties, particularly its hydrophilicity and solubility. additionally, the effect of temperature during both pre-gelatinization and drying processes is clearly evident, highlighting the importance of controlling these conditions to achieve an optimal structure in the treated starches. the findings from this study not only enhance our understanding of the rheological behavior of starch but also offer insights for optimizing industrial processes related to the production and application of this modified starch.