Evaluating the Effect of Selected Soaking Pretreatments On
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EVALUATING THE EFFECT OF SELECTED SOAKING PRETREATMENTS ON THE COLOR QUALITY AND PHENOLIC CONTENT OF PURPLE POTATO CHIPS THESIS Presented in Partial Fulfillment of the Requirements for the Degree Master of Science in the Graduate School of The Ohio State University By KAI ZHANG Graduate Program in Food Science and Technology The Ohio State University 2017 Master’s Examination Committee: Dr. M. Monica Giusti, Advisor Dr. Christopher T. Simons Dr. Lynn C. Knipe Copyrighted by Kai Zhang 2017 Abstract Purple potato chips made from natural potato varieties with purple-bluish flesh are a novel alternative product to traditional potato chips. However, color loss and anthocyanin degradation occur during the processing of purple chips due to high frying temperature and Maillard browning. The objective of this study was to evaluate the influence of pretreatment soaking solutions on the color formation and phenolic content of purple potato chips. Purple potatoes (Purple majesty) were obtained from a local market in Columbus (OH, USA), and cut into slices of 2±0.2 mm. After washing in running water, slices were soaked in solutions of citric acid, acetic acid, sodium chloride (NaCl) or calcium chloride (CaCl2) using four different concentrations (0.1%, 0.2%, 1%, 2%) for 10 minutes, superficially dried and fried for 3 minutes in vegetable oil at 170 °C. Color (CIELab), monomeric anthocyanins, and total phenolics were monitored on the final product. Potato slices pretreated with 1% and 2% citric acid solutions had brighter purple-bluish color (L*=39.1±0.4, h*=317.9°±3.6°) with less browning compared to samples pretreated with other solutions (L*=22-33, h*=306˚-329˚). Potato chips pretreated with 1% and 2% citric acid solutions had higher monomeric anthocyanin content (50.3-63.7 mg Cyanidin- 3-glucoside equivalents /100g fries) and less polymeric anthocyanin color ii (25.4-35.7%) as compared to other samples (monomeric: 30.6-44.6 mg/100g Cyanidin-3- glucoside equivalents, polymeric: 51.4-69.4%). Soaking treatments had less impact on total phenolics. The phenolic content of potato chips with 1% and 2% citric acid ranged from 538.5-554.7 mg gallic acid equivalents (GAE)/100g chips, against 400.7-519.1 GAE mg/100g in other soaked samples. The major anthocyanin in raw purple potatoes was identified by HPLC as Petunidin-3-(p- coumaroyl)-rutinoside-5-glucoside which remained unchanged during the processing, along with Petunidin-3-(caffeoyl)-rutinoside-5-glucoside and Malvidin-3-(p-coumaroyl)- rutinoside-5-glucoside as minors. Potato chips were vacuum packed and stored at room temperature in the dark. Longer storage period resulted in the accumulation of polymerized anthocyanins in the purple potato chips. Changes in the phenolic content of chips remained constant around 520 mg gallic acid equivalents (GAE) /100g dry weight. Reducing sugar content in potato slices decreased from ~3.4 to 2.6 g/100g DW with water rinsing. Most soaking treatments helped decrease sugars levels even further, as low as ~1.0g/100g DW with citric acid. Citric and acetic acid soaking solutions had pH levels below 4, especially in 1% and 2% citric acid solutions (pH 2). This may have helped retain color and monomeric anthocyanin content, particularly on potato chips pretreated with 1% and 2% citric acid, since anthocyanins are inherently more stable under acidic conditions. Citric acid’s ability to function as an acidulant resulted in greater benefit as compared to other pretreatment chemicals tested. In conclusion, soaking colored potato slices in citric acid could be used as pretreatment to enhance the color and phenolic quality of fried purple potato chips with potential application on industrial scale. iii Dedication This document is dedicated to my family. iv Acknowledgements I would like to thank my advisor, Dr. M. Monica Giusti, for her generous support with encouragement, knowledge and time during the entire master program. I greatly appreciate her guidance of great patience through my experiment and assistance in writing my thesis. I would like to thank Dr. Christopher T. Simons and Dr. Lynn C. Knipe for kindly being my committee and giving pertinent advice on my thesis. I would like to thank Mr. Steven Simons and the Food Industries Center of The Ohio State University for his help on the material preparation of this research. Finally, thanks my parents and my sister for their enduring love and metal support on my study. v Vita September 22nd, 1989……………………………….Born – Zhengzhou, Henan China 2015…………………………………………………B.S. Food Science and Technology, The Ohio State University 2015-2017…………………………………………...M.S. Food Science and Technology, The Ohio State University Fields of Study Major Field: Food Science and Technology vi Table of Contents Abstract ...................................................................................................................................... ii Dedication………………………………………………………………………………………………………iv Acknowledgements ................................................................................................................. v Vita .............................................................................................................................................. vi List of Figures ............................................................................................................................ x List of Tables ............................................................................................................................ xi Chapter 1 Introduction .......................................................................................................... 1 Chapter 2 Literature Review ............................................................................................... 3 2.1 Potato Chips .................................................................................................................................. 3 2.2 Potato Chips Production ............................................................................................................. 4 2.3 Potato Chips Color ....................................................................................................................... 5 2.3.1 Color Formation – Maillard Reaction ............................................................................................. 5 2.3.2 Color Parameters .................................................................................................................................... 6 2.4 Process Variables Affecting Chips Color ................................................................................ 7 2.4.1 Frying Temperature ............................................................................................................................... 7 2.4.2 Frying Time ............................................................................................................................................. 8 2.4.3 Storage Conditions ................................................................................................................................ 8 vii 2.4.4 Slice Thickness .................................................................................................................................................. 9 2.5 Cooking Methods Affecting Chip Color and Phenolic Contents ..................................... 10 2.5.1 Vacuum Frying .................................................................................................................................... 10 2.5.2 Baking ..................................................................................................................................................... 11 2.5.3 Microwaving ......................................................................................................................................... 12 2.6 Pre-treatments Prior to Frying Affecting Chips Color and Phenolic Contents ........... 12 2.6.1 Blanching ............................................................................................................................................... 12 2.6.2 Pre-drying .............................................................................................................................................. 14 2.6.3 Soaking ................................................................................................................................................... 15 2.7 Colored-flesh Potatoes ............................................................................................................... 17 2.7.1 Potato Varieties and Characteristics ............................................................................................. 17 2.7.1.1 Potato History and Composition ............................................................................................................ 17 2.7.1.2 Potato Varieties and Pigmented Cultivars ........................................................................................... 19 2.7.2 Anthocyanins ........................................................................................................................................ 20 2.7.2.1 Anthocyanins Structure ............................................................................................................................. 20 2.7.2.2 Anthocyanins in Pigmented Potatoes .................................................................................................... 22 2.7.2.3 Potential Health Benefits of Anthocyanin-rich Potatoes ...............................................................