Graduate Thesis Or Dissertation
 

The potato : composition, non-enzymatic browning and anthocyanins

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  • Chipping varieties and model systems were used to determine the role of potato constituents on chip color. Composition was evaluated by HPLC and chip color measured using a ColorQuest colorimeter. Reducing sugar (RS) content did not completely explain color quality when present in low concentrations (<60 mg/lOOg). Levels of ascorbic acid, glutamine and a chlorogenic acid isomer, along with RS, showed high correlation with color. Sucrose was a poor estimator of chip color. Model systems used leached potato slices infiltrated with solutions containing sucrose, RS, ascorbic, chlorogenic and amino acids. Linear association of RS with L* and hue angle and quadratic relationship with chroma of chips were found. Ascorbic acid affected chroma and hue at low RS levels while chlorogenic acid was not involved in color development. Red potatoes {Solarium tuberosum and Solarium stenotomum) were evaluated as potential source of natural red colorant. Cultivars (33) were screened for anthocyanin content and qualitative composition. Monomeric anthocyanin content, determined by pH differential, ranged between 4 and 40 mg/lOOg fresh weight (fw) tuber. Varieties 5847-1 and ND04069-4 showed high anthocyanin content (>35 mg/lOOg). Anthocyanin composition was characterized by HPLC, spectral analysis and Mass Spectroscopy (MS). The major anthocyanin was pelargonidin-3-rutinoside-5-glucoside acylated with p-coumaric acid. The presence of glycoalkaloids (α-solanine and α-chaconine) was detected by MS and quantified by HPLC. Varieties NDO4069-4 and 5847-1 showed glycoalkaloid levels of 13 and 7 mg/lOOg fw, respectively. Glycoalkaloids were precipitated from pigment concentrates by alkaline treatment. The best results were obtained at pH 8.0 with 30% monomeric anthocyanin degradation and 90% glycoalkaloid precipitation. The color and pigment stability of chemically related anthocyanin extracts (red-fleshed potatoes and radishes), the effect of pigment purity, and temperature were evaluated in model juices (pH 3.5). Color (CIELch) and anthocyanin degradation was monitored for 65 wks of storage. All model juices showed color similar to FD&C Red # 40. Excellent stability was obtained with all treatments in refrigeration. Anthocyanin structure and extraction method affected pigment stability. At 25°C, higher stability was obtained on juices colored with chemically purified radish anthocyanins (22 wk half-life) and lowest with potato vegetable juice (10 wk half-life).
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