Commercial wheat, corn and rice starch were extrusion cooked under a specific mechanical energy input (SME) ranging from 81 to 365 Wh/kg (288 to 1314 kJ/kg). Extrusion cooking at low and high SME resulted in products having significant differences in molecular weight distribution and having crystalline structures of the V-and E-type, as determined by gel permeation chromatography and X-ray diffraction analysis. Differential scanning calorimetry revealed that the glass transition temperature (T g ) of the extruded starches was independent of the botanical source, the degree of extrusion-induced molecular fragmentation and the formation of the V-and E-type crystalline structures. The obtained master curve, defined by the relationship between water content and T g of the amorphous starch, may be used as a predictive tool in modelling the extrusion process of starch or starch containing blends, especially with regard to the formation of the morphological structure and texture attributes of directly expanded products.
To elucidate the salt action in breakfast cereals to decrease its amount without a quality loss, a model system was developed. This model, composed of native maize starch, glucose and a mixture of five amino acids (glucose ⁄ amino acids molar ratio = 1 ⁄ 1) generated similar colour and volatiles (m ⁄ z = 45, 59, 69, 73, 87 and 103 g mol )1 ) after heating compared to commercial breakfast cereals. A designed experiment used this model to study the influence of salt concentration (0-5.44%), heating time (0-25 min) and temperature (180-230°C) on colour, residual volatiles and acrylamide formation. The higher the salt concentration, heating time and temperature, the darker were the products (P < 0.05). The L* values of the model systems containing 5 % salt and heated for 25 min at 230°C were twelve points lower than the same systems without salt heated in the same conditions. Presence of salt significantly decreased acrylamide formation in the model systems (up to 50 % decrease when 2.5 % salt is added). However, salt did not have a significant impact on volatile levels. These findings were confirmed by observations made on four types of commercial breakfast cereals.
Research efforts aim to enhance fundamental understanding about the role of salt in cereal products. Such knowledge may open new strategies for salt reduction in respective product categories. A model system, containing pregelatinized starch, glucose, and amino acids heated at 230°C for up to 10 min demonstrated that NaCl leads to darker products compared with the same model heated without NaCl (P < 0.05). The same trend was observed in wheat breakfast cereal flakes toasted at 230°C. The present study investigated two hypotheses how salt may influence color formation through Maillard Reaction: 1) hygroscopic behavior of salt may change the retention of water during heating and encourage Maillard reactions by improving mobility of reactants; 2) salt has a plasticizing effect and the presence of salt might keep the product in a rubbery state longer while heating, hence improving mobility and Maillard reactions of reactants. The same models (pregelatinized starch, glucose, and amino acids) mixed with several types of plasticizers (NaCl, KCl, or trehalose) and a blank without plasticizer were made and heat‐treated under controlled conditions. The presence of plasticizers always led to darker products but no correlation was found between color formation, the hygroscopic behavior of the system, and its glass transition temperature as measured by phase transition analyzer.
To reduce the amount of salt in cereal‐based products without changing their properties, it is necessary to understand the role of salt in the product. Native wx maize, cassava or potato starch were mixed with sodium chloride (NaCl; 0–4% dry weight basis; moisture adjusted to 20% wet weight basis; wwb) and were heated at 230°C for 45 min. Presence of salt enhanced colour formation proportionally to its concentration. Microscopic observations, wide angle X‐ray, DSC and intrinsic viscosity data all suggested that the starch granule and the starch polymer were degraded by such heat treatment. Presence of NaCl enhanced the degradation proportionally to its concentration. This degradation might lead to the formation of smaller molecules which potentially could then caramelise during the heat treatment. This mechanism may explain the impact of salt on colour formation in cereal‐based products.
A previous study demonstrated that presence of sodium chloride enhanced colour formation and starch degradation during heat treatment of a starch based model. It was suggested that the presence of salt encouraged breakdown of the starch, at all levels of organisation, including depolymerisation of the glucose chains to generate smaller molecules, such as glucose. These then would caramelise, explaining the impact of salt on colour formation during the heat treatment of these models. This study aimed at investigating the influence of several types of salt on starch degradation and caramelisation. Native wx maize starch (100 g dry weight) was mixed with 0.030 mol of salt (NaCl, KCl, CaCl2, LiCl, MgCl2, NaI, KNO3, NaBr, KBr, Na2SO4, NaNO3, Na2CO3 or KI, moisture adjusted to 20% wet weight basis). These samples were heated at 230°C for 30 min. The presence of salts significantly enhanced colour formation and the starches' loss of crystallinity during the heat treatment (p < 0.05). NaCl, KCl, CaCl2 and MgCl2 increased significantly the colour formation via caramelisation reactions (p < 0.05). The potency of the salt depended on the salt's cations and followed the Hofmeister series. However, anion variation did not have any significant influence on starch crystallinity loss and colour development. The type of salt also affected colour formation when heated with glucose thereby indicating that the colour reaction, as well as starch changes, is influenced by the ionic environment. Presence of salt might enhance starch degradation either by a direct interaction with the starch granule, or indirectly by accelerating the caramelisation reactions which then produces acidity which helps degrade the starch granules.
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