Abstract
The effects of a range of barrel dry heat temperatures (20 to 180 oC), and moist heat pressure (MHP) (120 oC 15 min 192 kPa) on Maillard reaction product (MRP) formation and canola meal structural characteristics were investigated. Increasing dry heat temperature was negatively correlated with meal whiteness L* and yellowness b* (early-MRP) and positively with surface hydrophobicity. Relative to control meal, MHP increased early-MRP, redness, browning index (late-MRP), and acidity; and decreased L*, surface hydrophobicity, b*, and Abs294nm (intermediate-MRP). Dry heat-associated changes in surface hydrophobicity suggest protein unfolding and side-chain modifications. Lack of high MW polypeptides at dry heat temperatures of 160 and 180 oC imply protein denaturation and formation of insoluble polypeptides. Specific dry heat temperatures increased surface lipid and induced the formation of protein matrix and aggregation. Meal surface morphology rounded and flattened at specific dry heat temperatures, and smoothed with MHP. Differences in lipid-related functional groups were evident between dry heat temperatures, and with MHP. Treatment with MHP affected amide I and II, α-helix, β-sheet, their respective ratios and the total protein fingerprint region; fragmented meal into proteolysis-resistant protein aggregates with crevices containing lipid droplets; and, reduced solubility of canola meal polypeptides > 40 kDa. The changes observed may have a great effect on ruminal degradation and supply of protein and AA for ruminant utilisation.
Highlights
Canola meal is a derivative of seed oil production utilised as a protein supplement in dairy cattle (Sánchez & Claypool, 1983; Santos, 2011) and feedlot (He et al, 2013; Williams et al, 2008) rations
The effects of dry heat (20 to 180 oC) with moist heat pressure (MHP) on Maillard reaction products (MRP) formation and structural characteristics of canola meal are presented in Table 1
As dry heat temperature increased the yellowness of meal decreased (b*, rs = -0.65, P < 0.05), whiteness decreased (L*, rs = -0.77, P < 0.05), and redness remained similar (a*, rs = 0.56)
Summary
Canola (rapeseed, Brassica spp. napus, rapa, and juncea) meal is a derivative of seed oil production utilised as a protein supplement in dairy cattle (Sánchez & Claypool, 1983; Santos, 2011) and feedlot (He et al, 2013; Williams et al, 2008) rations. To extract seed oil and generate meal, solvent-based and mechanical (e.g., cold-press, expeller, and extrusion) processing technologies exist. Expeller extraction utilises dry heat (95 to 135 oC) (Newkirk, 2009), and, cold-press extraction mechanically presses seeds by frictional force ( 65 oC) (Leming & Lember, 2005). The formation of heat-damaged protein from the Maillard reaction during processing is of concern for ruminant nutritionists, as it contributes to ruminal insoluble undegraded CP (RUP) levels without providing nutritional benefit (Ross et al, 2013). Acid detergent insoluble nitrogen (ADIN) was utilised to monitor heat-damage protein; ADIN does not quantitatively account for all Maillard reaction products (MRP). It is of interest to quantify production of MRP during processing of canola meal utilising other established techniques, for instance pH, UV/Vis absorbance at 294 nm (Ajandouz et al, 2001), colorimetry, and gel electrophoresis (Liu et al, 2014)
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