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Functional Structure/Activity Relationships
Maillard-reacted whey protein isolates enhances thermal stability of anthocyanins over a wide pH range Xinguang Qin, Dan Yuan, Qi Wang, Zhongze Hu, Yang Wu, Jie Cai, Qingrong Huang, Shuyi Li, and Gang Liu J. Agric. Food Chem., Just Accepted Manuscript • Publication Date (Web): 14 Aug 2018 Downloaded from http://pubs.acs.org on August 14, 2018
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Heat Stability of Anthocyanins 0.0
ln(Ct/C0)
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C3G pH=6.0 C3G with WPI-Glu pH=6.0 C3G pH=3.0 C3G with WPI-Glu pH=3.0
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Time (min) C3G
WPI-Glu
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Maillard-reacted whey protein isolates enhances thermal stability of
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anthocyanins over a wide pH range
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Xinguang Qina, Dan Yuana, Qi Wanga, Zhongze Hua, Yang Wu a, Jie Caia, Qingrong Huangb, Shuyi Lia,
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and Gang Liu*a
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a
College of Food Science and Engineering, Wuhan Polytechnic University, Wuhan, China, 430023;
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b
Department of Food Science, Rutgers University, 65 Dudley Road, New Brunswick, New Jersey 08901, United
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States
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Corresponding author:
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*Gang Liu
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E-mail:
[email protected] 15 16 17 18 19 20 21 22 23 24 25
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Abstract
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The poor thermal and acid stabilities of anthocyanins greatly limit their industrial
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applications as functional food ingredients. This work investigated the ability of the
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Maillard reaction products (MRPs) of whey protein isolates and glucose to enhance
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the thermal stability of anthocyanins over the pH range of 2.0 to 7.0. Anthocyanin
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dispersions were subjected to up to 80 min of thermal treatment at 80 °C. The
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improvement in the color stability and antioxidant capacity of the anthocyanin
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dispersions indicated that MRP remarkably inhibited anthocyanin degradation.
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Fluorescence spectroscopy results suggested that anthocyanins and MRPs form
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complexes through hydrophobic interactions. These complexes effectively attenuated
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anthocyanin degradation under heat treatment at pH 6.0. The particle sizes of MRPs
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alone or in complex with anthocyanins remained unchanged after heating. The novel
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protein delivery system proposed in this study expands the applications of
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anthocyanins as acid- and heat-stable functional food ingredients.
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Key words: Anthocyanins, heat stability, degradation, whey protein, Maillard
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reaction
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1. Introduction
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Anthocyanins are ubiquitous water-soluble pigments that confer colors to most
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vegetables and fruits 1. These compounds are present in various food products and
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have excellent biological activities that benefit human health, including antioxidant1,
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anticancer, and anti-inflammatory properties.2 Moreover, anthocyanins exert
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neuroprotective effects and promote skin health3. Anthocyanins have poor color and
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structural stability and may be readily hydrolyzed into colorless compounds when
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subjected to unfavorable environments4, 5. pH, temperature, oxygen, pressure, light,
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enzymes, and metallic ions are some factors that affect anthocyanin stability6. In
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particular, the color of anthocyanin solutions changes from pink to red, violet, or blue
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as system pH increases1.
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Anthocyanins are only thermally stable at pH 80 °C7. Enhancing the stability of anthocyanins at
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pH ≥3 during storage and processing is the bottleneck in the industrial application of
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these compounds. The loss of color stability under acidic conditions may be attributed
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to hydration on the 2-position of the anthocyanidin skeleton8. This loss is particularly
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pronounced
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copigmentation, encapsulation, and metallic ion addition1, have been applied to
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enhance anthocyanin stability. Copigmentation, a popular approach, commonly
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involves complexing anthocyanins with biomacromolecules10 that can enhance
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anthocyanin stability over a certain pH range. For example, complexation with
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β-cyclodextrin enhances the stability of anthocyanins derived from chokeberry at pH
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2.8–3.611, and gum arabic enhances the thermal stability of anthocyanins at
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temperatures of 80 °C and 126 °C and pH 5.012. Furthermore, yeast mannoproteins
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enhance anthocyanin stability at pH 7.013. When added to alginate, Fe3+ prevents the
at
pH
>4.59.
Numerous
strategies,
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degradation and aggregation of anthocyanins subjected to heat treatment at 60 °C for
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up to 80 min at pH ≤7.0; this result may be attributed to complexation14. Pectins and
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biopolymers, such as proteins, can retard anthocyanin degradation. Although proteins
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can better stabilize anthocyanins than pectins,15 they may form large aggregates and
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increase solution turbidity after thermal treatment at pH 5.0 near the isoelectric point
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(PI) of the protein. Glycation increases the thermal stability of whey protein isolate
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(WPI) over the pH range of 2.0–7.0 because the grafted groups on saccharides exert
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steric hindrance that inhibits protein folding under heat treatment16, 17. Nevertheless,
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reports on the effects of copigmentation on the stabilization of anthocyanins over pH
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3.0–7.0 are scarce. Moreover, few studies have investigated the effects of Maillard
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reaction products (MRPs) on the heat stability of anthocyanins over pH 3.0–7.0.
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The present study investigated the potential application of MRPs, such as whey
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WPI glycated with glucose (WPI–Glu), to enhance the thermal stability and maintain
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the physicochemical characters of anthocyanins over pH 3.0–7.0. WPI is an ideal food
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ingredient with high essential amino acid content18. We previously showed that WPI
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glycated with saccharides, such as Glu, lactose, or maltodextrin, exhibits good heat
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stability over the broad pH range of 3.0–7.0 and even at a pH value near the PI. At pH
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