Impact of Processing on the Physicochemical and Nutritional Properties of Intermediate Wheatgrass (Thinopyrum intermedium) and Wheat (Triticum sp.)

Abstract

Annual cereal grains are a major part of the human diet. However, their cultivation is less sustainable and is associated with environmental issues such as soil erosion and emission of greenhouse gases into the atmosphere. Cultivating perennial grain crops to supplement these annual grains offers a promising approach to reducing these environmental issues while providing food for the ever-growing human population. To this end, intermediate wheatgrass (IWG), a perennial grain crop, is being developed and explored for mainstream food applications. The first part of this dissertation explored extrusion cooking of IWG for the first time to produce expanded IWG that could be used as snacks and breakfast cereals. First, we optimized the extrusion conditions for the production of expanded IWG. In that work, the effects of extrusion conditions including feed moisture content (20, 24, and 28%), screw speed (200, 300, and 400 rpm), and extrusion temperature (130, 150, and 170 °C) on the physical and functional properties (moisture content, expansion ratio, bulk density, hardness, water absorption index (WAI), water solubility index (WSI)) of IWG were investigated. Response surface methodology (RSM) was used to model and optimize the extrusion conditions to produce expanded IWG. The model coefficient of determination (R2) was high for all the responses (0.87 – 0.98). All the models were found to be significant (p < 0.05) and were validated with independent experiments. Generally, all the extrusion conditions were found to have significant effects on the IWG properties measured. Increasing screw speed and decreasing the extrusion temperature resulted in IWG extrudates with high expansion ratio. This also resulted in IWG extrudates with generally low hardness and bulk density. Screw speed was found to have the most significant effect on water absorption index (WAI) and water solubility index (WSI), with increasing screw speed resulting in a significant (p < 0.05) decrease in WAI and a significant (p < 0.05) increase in WSI. The optimum conditions for obtaining an IWG extrudate with a high expansion ratio and WAI were found to be 20% feed moisture, 200 – 356 rpm screw speed, and 130 – 154 °C extrusion temperature. Then, these optimum conditions were used to produce two expanded IWG products (extrudates I and II), and the physicochemical and nutritional properties of these products were characterized, comparing them to raw IWG flour. We observed that extrusion resulted in slight decreases in dietary fiber, fat, starch, and amylose contents of IWG, whereas protein and ash contents did not change. A significant increase in starch damage after extrusion led to significant increases in starch digestibility and hydration properties of IWG. Correspondingly, slowly digestible starches and resistant starches were significantly reduced after extrusion. Pasting profile studies showed significant decreases in all pasting parameters measured except for breakdown viscosity after extrusion. Higher antioxidant activity and phenolic acid levels, mainly due to ferulic acid, were observed even after extrusion. However, carotenoid content decreased significantly (up to 65.8% reduction in lutein and 50.4% reduction in zeaxanthin). These findings provide useful information on the production of expanded IWG using extrusion cooking. This is critical in the efforts to increase the demand and marketability of IWG. Furthermore, we have shown that extrusion cooking can improve the antioxidant activity and maintain high protein and dietary fiber levels in IWG, but it may not be suitable for preserving carotenoids in IWG.In the second part of this dissertation, we aimed to address an issue with the consumption of wheat, an annual grain that is a major staple worldwide. Wheat provides nearly 20% of calories and protein in the human diet. However, fermentable oligo-, di-, and monosaccharides and polyols (FODMAPs) and amylase/trypsin inhibitors (ATIs) present in wheat flour can trigger irritable bowel syndrome (IBS) and non-celiac wheat sensitivity (NCWS) symptoms in some individuals. This has negatively affected the demand and consumption of wheat in recent years. Thus, reducing FODMAPs and ATI concentrations in wheat flour could make the grain accessible to humans with IBS or NCWS. To this end, we first evaluated a diverse panel of heritage and modern spring wheat lines (208 lines in total) grown in two locations in Minnesota (Crookston and Saint Paul) for FODMAPs and ATI levels and carried out a genome-wide association analysis to identify markers associated with wheat FODMAPs and ATIs. The discovery of such markers, in conjunction with a genome-wide selection strategy, could aid in the selection of breeding lines with lower levels of FODMAPs and ATIs. FODMAPs and ATIs were quantified using High-performance anion-exchange chromatography (HPAEC) and High-performance liquid chromatography (HPLC), respectively. A strong population structure was observed, as the first principal component axis alone explained a third of the genotypic variation, and lines clustered into three distinct clusters of einkorn, emmer, and modern wheat lines. Trait correlations (r) were low to moderately high, ranging from 0.06 - 0.54. Broad-sense heritabilities ranged from low to medium (0.18 - 0.55). Association analysis resulted in the detection of 36 quantitative trait loci (QTL) in 15 chromosomes which were distributed in 30 unique genomic regions based on haplotype analysis; five of the 36 QTL were shared among two to four traits. The QTL were of small to medium effect as the range of explained phenotypic variation was 6.4% - 10.5%. There was no overlap among the QTL regions reported in this research compared with those reported in previously published studies. Genomic prediction models predicted the traits with low to moderately strong correlations (r = 0.23 - 0.49). We also investigated the effect of type I sourdough fermentation (4- and 12-h fermentation times) on the FODMAP and ATI levels in twenty-two wheat lines selected from the lines used in the genetics study based on availability and the initial levels of these compounds. We observed that FODMAPs and ATIs were significantly influenced by variety as well as growing location. Longer sourdough fermentation time (12 h) caused up to 69%, 69%, and 41% reductions in fructans, raffinose, and ATIs, respectively, in the resulting sourdoughs. However, a substantial increase in mannitol (550%) was observed after sourdough fermentation. These findings suggest that in type I sourdough fermentation, mannitol production should be monitored, and strategies to reduce its level in the fermented product should be considered.