Wajira S. Ratnayake

Chapter 5 Starch Gelatinization

Starch occurs as highly organized structures, known as starch granules. Starch has unique thermal properties and functionality that have permitted its wide use in food products and industrial applications. When heated in water, starch undergoes a transition process, during which the granules break down into a mixture of polymers-in-solution, known as gelatinization. The sequence of structural transformations that the starch granule undergoes during this order-to-disorder transition has been extensively researched. None of the published starch gelatinization theories can fully and adequately explain the exact mechanism of sequential structural changes that starch granules undergo during gelatinization. This chapter analyzes several published theories and summarizes our current understanding of the starch gelatinization process.

Characterisation and potential application of pineapple pomace in an extruded product for fibre enhancement

This study characterised pineapple pomace (PP) and evaluated its application in extrusion to enhance fibre content of the final product. The pomace had low fat (0.61%) and high dietary fibre (45.22%), showing its potential for fibre enrichment of nutritionally poor products, as some extruded snacks. Results also showed low microbiological counts, water activity, and pH indicating good microbiological quality and low risk of physicochemical deterioration. During extrusion, pomace (0%, 10.5% and 21%), moisture (14%, 15% and 16%) and temperature (140 and 160°C) were evaluated. The PP addition decreased expansion and luminosity; while increasing redness of the extrudates compared to the control (0% pomace/14% moisture/140°C). When hardness, yellowness, water absorption, and bulk density were compared to the control, there was no effect (p>0.05) of 10.5% PP addition on the extrudates, indicating that, at this level, PP could be added without affecting the properties of the final extruded product.

Thermal behavior of resistant starches RS 2, RS 3, and RS 4.

The thermal behaviors of 3 resistant starch types-RS 2, RS 3, and RS 4-were investigated. Samples were heated in excess water to specific temperatures, from 35 to 85 degrees C at 5 degrees C intervals, and freeze-dried. The treated samples were analyzed using SEM, DSC, XRD, and HPSEC to determine the structural changes at granular and molecular levels. Light microscopy was used to determine real-time thermal behavior of the starches. Although the resistant starches did not show significant morphological changes, as revealed by microscopy, they underwent internal structural changes at low temperatures before complete phase transitions occurred. The structural changes were less in RS 2 compared to the other 2 starches studied. The nongranular material of RS 3s crystallinity decreased gradually from 35 to 85 degrees C and showed microscopically visible changes at >80 degrees C. Cross-linking might have prevented RS 4 from becoming completely amorphous within the temperature range (35 to 85 degrees C) tested. The study indicated that the extent of structural changes depended on the treatment temperature and RS type.

Extraction and Characterization of Starch from Alkaline Cooked Corn Masa

ABSTRACT Starch granules undergo structural and morphological changes during food processing unit operations as they interact with other food ingredients. This study was conducted to isolate and characterize starch granules from corn masa. A proteolytic enzyme, thermolysin, was effective in separating and isolating starch granules from endosperm proteins present in masa. The efficiency of starch extraction using thermolysin was 74% (w/w), and subsequent analyses showed that the isolated granules were free of contaminants. Starch samples were characterized using light microscopy, SEM, DSC, and XRD. Starch granules isolated from masa had undergone internal structural changes and some granules (≈40%) lost birefringence during nixtamalization. These internal changes occurred, in most cases, without visible alterations in general granular morphology. Nixtamalized granules underwent changes mostly consistent with a “heat-moisture treatment” process.

Factors affecting the alkaline cooking performance of selected corn and sorghum hybrids.

ABSTRACT Dent corn (Zea mays L.) and sorghum (Sorghum bicolor L. Moench) sample sets representative of commonly grown hybrids and diverse physical attributes were analyzed for alkaline cooking performance. The influence of kernel characteristics including hardness, density, starch properties (thermal, pasting, and crystallinity), starch content, protein content, and prolamin content on alkaline cooking performance was also determined. Corn nixtamal moisture content was lower for hard, dense kernels with high protein contents; sorghum nixtamal moisture content was lower for kernels with low moisture contents and low starch relative crystallinities. Statistically significant (P < 0.05) regression equations showed that corn nixtamal moisture content was influenced by TADD (tangential abrasive dehulling device) index, kernel moisture content, starch content, and protein content; sorghum nixtamal moisture content was influenced by starch relative crystallinity, kernel moisture content, and abrasive hardness in...

Physicochemical and Thermal Properties of Phaseolus vulgaris L. var. Great Northern Bean Starch

UNLABELLED The compositions and properties of 5 Great Northern bean cultivars (Beryl-R, Coyne, Gemini, Marquis, and Orion) were investigated. Starch was isolated from each cultivar by a wet milling process. Isolated, unmodified starches were characterized for granular, molecular, thermal, and rheological properties. Smooth surfaces and essentially similar granule sizes and shapes were observed among all cultivars. Amylose contents were in the range 21.0% to 22.6%. Amylose and amylopectin molecular weights were approximately 10(5) and 10(9) Da, respectively. Typical C-type X-ray pattern was observed in all cultivars. Significant differences were observed among cultivars in percentage relative crystallinities, which were in the range 18.2% to 23.8%. The relative crystallinity was independent of amylose proportion and molecular weight. The 5 Great Northern bean cultivars differed in their thermal and rheological properties. Coyne and Gemini had low gelatinization enthalpies. In pasting profile analysis, Coyne had the lowest peak and final viscosities. Granule size, polymer proportion, and molecular weights had major influences on gelatinization and pasting properties of Great Northern bean starches. PRACTICAL APPLICATION Great Northern bean is one of the major varieties of dry-edible beans produced worldwide. Starch is the major component in Great Northern beans, which accounts for approximately 40% of its composition. Although most legume starches have been studied in detail, physicochemical and functional properties of Great Northern bean starch are largely unknown. This study investigated the properties and thermal behaviors of 5 Great Northern bean cultivars. The new information reported in this article, on starch properties, would pave ways to find new ingredient and product applications for Great Northern beans in food processing.

Assessment of Corn Quality for Nixtamalization: Development of a Convenient Bench-Top Cooking Method

A convenient small-scale laboratory method that can be used to simultaneously analyze multiple samples was developed to rapidly assess suitability of corn for nixtamalization. This new 100 g method was developed based on a previously reported 500 g laboratory process that has been shown to mimic the industrial nixtamalization process. The two methods were compared for nixtamal moisture, dry matter loss, degree of pericarp removal, and gelatinization properties of the cooked corn. The heating and cooling profiles of the 100 g method were developed using the 500 g method, by monitoring temperature every 30 s during cooking and steeping. Nixtamalization was conducted with a 1:4 corn/water ratio, with 1% lime. A response surface central composite design was used to model a wide range of processing conditions for the two methods: cook temperature (80–95°C), cook time (3–40 min), and steep time (2–12 h). Parameter estimates and response surfaces were compared, and predictive models were fitted. The response sur...

Great Northern Bean Could Improve the Nutritional Value of Instant Noodles

Instant noodles were prepared by substituting hard red winter (HRW) wheat flour with Great Northern bean powder (GNBP) at selected levels (0–60%) using a pilot-scale noodle processing machine. The functional properties, water absorption, water solubility, and pasting profiles of flour mixtures were tested to verify the process tolerances of ingredients. Prepared noodle samples were evaluated for color, cooking quality, texture, and sensory properties. Slight color differences, an increased cooking loss, and reduced chewiness, cohesiveness, and hardness were observed in cooked noodles that were prepared with GNBP up to 25% of HRW wheat flour weight. The results suggest that HRW wheat flour could be replaced up to 20% (w/w) with GNBP, while still using the conventional processing conditions, to improve the product nutritional value (i.e., increased protein and fiber contents and reduced fat content) (P < 0.05).