Physical, chemical and biochemical properties of casein hydrolyzedby three proteases: Partial characterizationsYangchao Luo, Kang Pan, Qixin Zhong ⇑Department of Food Science and Technology, The University of Tennessee, Knoxville, TN 37996, United Statesa r t i c l e i n f oArticle history:Received 6 October 2013Received in revised form 13 December 2013Accepted 15 January 2014Available online 23 January 2014Keywords:Sodium caseinateHydrolysatesProteasesEmulsifying propertyAntioxidant activityACE-inhibitory activitya b s t r a c tSodium caseinate (NaCas) was hydrolyzed by papain, pancreatin and trypsin from 10 min to 24 h, and thehydrolysates were partially characterized for several important properties. At the studied conditions,papain and trypsin were more effective in hydrolyzing NaCas than pancreatin. Pancreatin treatmentsshowed an initial increase in surface hydrophobicity, contrasting with the consistent decrease for theother two treatments. The solubility of NaCas at acidic pH was improved, becoming pH-independent after24 h hydrolysis. The emulsifying properties generally showed improvements after hydrolysis. The DPPHfree radical scavenging activity, reducing power, and inhibition of linoleic acid autoxidation were signif-icantly enhanced after appropriate hydrolysis, while metal ion chelating effects were slightly attenuated.The angiotensin converting enzyme-inhibitory activity was significantly improved by up to 9 times thanthat of NaCas. These findings indicate that physical, chemical and biochemical properties of caseinhydrolysates can be improved by selecting proteolytic conditions to produce functional ingredients.? 2014 Elsevier Ltd. All rights reserved.1. IntroductionProtein hydrolysates have attracted increasing attention sincelast decade because of the enhancement in functional propertiesand health-promoting bioactivities from their precursor proteins.The functionalities of particular interest include the improved sol-ubility, particularly at pH near the isoelectric point (pI), enhancedemulsifying properties, as well as enriched biological activities.Especially, due to bioactive peptides produced during enzymatichydrolysis, the health-promoting effects of hydrolysates, such asantihypertensive, antithrombotic, anticancer, immunomodulatoryand opioid activities have been extensively reported (Udenigwe& Aluko, 2012).Caseins are a group of soluble milk proteins and are present ascasein micelles consisting of a s1-, a s2-, b- and j -caseins, and theratio of the four caseins differs in mammals. Enzymatic hydrolysisof caseins has been reported to have improved functional proper-ties and bioactivities, with the extent depending on the proteasetype and hydrolysis time (López-Fandiño, Otte, & van Camp,2006). For instance, casein is well-known for its strong mineral-binding capability, but the poor solubility of casein-mineral com-plexes at gastrointestinal conditions results in low bioavailabilityof the minerals (Korhonen, 2009). An improvement in the bioavail-ability of zinc has been reported after forming complexes withenzymatic hydrolysates of yak casein (Wang, Zhou, Tong, & Mao,2011). The health-promoting benefits of yak casein, such as freeradical scavenging capacity and anti-inflammatory activity, werealso dramatically enhanced by proteolysis, with alcalase beingthe most effective enzyme, followed by trypsin (Mao, Cheng,Wang, & Wu, 2011). Similar improvements in health benefits werereported after the enzymatic hydrolysis of camel casein (Salamiet al., 2010) and ovine casein (Gómez-Ruiz, López-Expósito, Pihlan-to, Ramos, & Recio, 2008).Bovine milk is the most commonly consumed milk and is pro-cessed to various dairy ingredients and products. Sodium caseinate(NaCas) is a dairy ingredient developed to enhance functionalitiessuch as water solubility, emulsifying and foaming properties, aswell as encapsulation capabilities (Pan, Zhong, & Baek, 2013;Sánchez & Patino, 2005). NaCas has also been recently explored asa novel stabilizer and absorption enhancer of hydrophobic proteinnanoparticles (Luo, Teng, Wang, & Wang, 2013; Zhang et al., 2014).However, the solubility of NaCas at acidic pHs near the pI (aroundpH 4.6) is poor, and its biological activities are limited. Enzymatichydrolysis has recently been shown to enhance the bioactivities ofNaCas, including inhibition of angiotensin I-converting enzyme(ACE), antimicrobial properties and antioxidant capabilities (Chen& Li, 2012; Hogan, Zhang, Li, Wang, & Zhou, 2009).Despite numerous studies on the properties of casein hydroly-sates, the impact of proteolytic conditions on important physical,http://dx.doi.org/10.1016/j.foodchem.2014.01.0480308-8146/? 2014 Elsevier Ltd. All rights reserved.⇑ Corresponding author. Address: Department of Food Science and Technology,The University of Tennessee, 2510 River Drive, Knoxville, TN 37996, United States.Tel.: +1 (865) 974 6196; fax: +1 (865) 974 7332.E-mail address: qzhong@utk.edu (Q. Zhong).Food Chemistry 155 (2014) 146–154Contents lists available at ScienceDirectFood Chemistryjournal homepage: www.elsevier.com/locate/foodchem
