Impact of cooking method on the protein quality of Russet potatoes
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Prior research has found that even though the amount of protein within potatoes is low (average of 2% w/w), due to the high consumption of potatoes in North America, it is estimated that they provide 2-4% of daily protein intake. Thus, potatoes are an important contributor for protein in diets. However, research is limited on the impact of cooking method on the quality of the protein in Russet potatoes, a major potato varietal. The current study was designed to address this knowledge gap. Russet potatoes were secured and subjected to the following cooking conditions (3 replicates per condition): raw, boiled, baked, microwaved and fried (3, 6 and 9 minutes). Following cooking, samples were analyzed for crude protein (CP) and total amino acids (AA; 3 hydrolysis conditions) by AOAC methods, in vitro protein digestibility (%IVPD) by pH-stat analysis, and in vivo protein digestibility by AOAC methods determining true fecal protein digestibility (TPD). In vitro protein digestibility-corrected amino acid score (PDCAAS) values were determined as the product of AAS and %IVPD. For %CP, on an as-consumed basis, with the exception of boiled, all cooking methods yielded higher (p<0.0001) values than the RAW samples. (RAW=1.85±0.04; BOIL=1.67±0.04); MICRO= 2.99±0.06; BAKE=2.44±0.03; FRIED3M=3.07¬±0.07; FRIED6M=3.87±0.03; FRIED9M=4.77±0.08). The AAS of raw potato was 0.66±0.01 with histidine as the first limiting AA. The AAS for the fried cooking methods (FRIED3M=0.474±0.009; FRIED6M=0.044±0.012; FRIED9M=0.36±0.015) as well as BAKE (0.57±0.045) were significantly lower than the RAW control (p=<0.05). The other AAS (BOIL=0.675±0.03; MICRO=0.589±0.008) were not significantly different from RAW. Based on 1-way ANOVA, there was a significant (p<0.05) main effect of cooking method on %IVPD except for BOIL and FRIED9M when compared to RAW (RAW=74.1±0.6; BOIL=74.3±0.5; FRIED9M=76.6±1.7; MICRO=78.1±2.3; BAKE=79.2±1.0; FRIED3M=78.4±0.6; and FREID6M=78.0±0.7). IVPDCAAS was lowest for FRIED9M=27.7±1.8, while BOIL=50.2±0.4 was the highest. The TPD was impacted by cooking methods, with values being: MICRO = 0.49; BAKE = 0.53; and BOIL = 0.56, which were all significantly higher than values observed for RAW (0.27) and FRIED6M (0.29). To summarize, cooking methods can significantly influence protein quality, with longer frying times leading to lower quality scores. Based on the limiting AA profile, potatoes are complementary protein sources to pulses and cereals, however frying can negatively impact potato protein quality.