E: Food Engineering & Physical Properties JFS E: Food Engineering and Physical Properties Proteolytic and Rheological Properties of Aging Cheddar-Like Caprine Milk Cheeses Manufactured at Different Times during Lactation D.L. V AN HEKKEN, M.H. T UNICK, K.A. SORYAL, AND S.S. ZENG ABSTRACT: The effects of 24 wk of aging on the proteolytic and rheological properties of cheddar-like cheese made from caprine milk collected at different lactation periods were evaluated. Cheddar cheese was made weekly using whole milk from Alpine goats and cheeses manufactured at weeks 4, 5, 12, 14, 15, 21, 22, and 23 of lactation were evaluated for proteolytic and rheological properties at 5 d after manufacture and after 8, 16, and 24 wk of aging at 4 ◦ C. Rheology results indicated that a minimum of 8 wk of aging was needed to stabilize the texture of the cheese and that the most uniform cheeses were made from mid lactation milk. Cheeses manufactured at weeks 12 to 15 of lactation were the firmest, had the least flexible protein matrix (highest values for hardness, chewiness, and shear stress and rigidity at point of fracture), and the lowest degree of proteolysis. Understanding the factors that impact the texture of cheese, such as aging and the period of lactation that cheesemilk is obtained, will help develop guidance for maintaining the production of high quality and uniform caprine milk cheeses. Keywords: caprine, cheese, goat milk, proteolysis, rheology Introduction T he manufacture of caprine milk cheese is a growing industry in the United States, and the production of high quality cheese is the key to its continued growth. Caprine milk products can be beneficial in diets of individuals who are allergic to bovine milk, and gourmet cheeses and other products made from caprine milk have an increasing appeal as people become more affluent (Haenlein 2001). In the United States, many goat herds are seasonal milk produc- ers (approximately 24 to 30 wk out of the year, early spring to late fall) and the milk available for making cheese on any one day would be from the same stage of lactation. The chemical composition of caprine milk changes as lactation progresses, with total solids, fat, and protein contents being the highest in the first month after partu- rition, gradually decreasing until weeks 20 to 25, and then increas- ing until the end of lactation (Tziboula-Clarke 2003). This pattern is influenced by many factors, including nutrition, breed, season, environment, and management practices. Zeng and others (1997) reported that for Alpine goats in a midwestern United States herd, the total solids, fat, and protein contents were highest at the be- ginning and end of lactation; lactose levels were elevated for the MS 20060416 Submitted 7/26/2006, Accepted 1/2/2007. Authors Van Hekken and Tunick are with Dairy Processing and Products Research Unit, Eastern Regional Research Center, USDA, ARS, 600 East Mermaid Lane, Wyndmoor, PA, 19038. Author Soryal is with Animal and Poultry Division, Desert Re- search Center, Matareya, Cairo, Egypt. Author Zeng is with E (Kika) de la Garza American Institute for Goat Research, Langston University, PO Box 1730, Langston, OK 73050. Direct inquiries to author Van Hekken (E-mail: diane.vanhekken@ars.usda.gov). Mention of trade names or commercial products in this article is solely for the purpose of providing specific information and does not imply recom- mendation or endorsement by the U.S. Dept. of Agriculture. 1st 2 mo and then declined to a lower level for the rest of the lacta- tion. They also reported that caprine milk produced between weeks 4 and 22 of lactation has the least variability in composition. Cheese texture is extremely important to the consumer and their acceptance of the cheese. The texture of the cheese is dependent on the components used to make the cheese matrix and the stabil- ity of the matrix. Although significant amounts of proteolysis occur in caprine milk cheese during aging (Jin and Park 1995; Kubis and others 2001), the impact of the degradation of the protein matrix on cheese texture was not examined in these studies. Rheology quanti- fies the texture of a food by measuring the food’s response to either large or small deformations (Tunick and Van Hekken 2002). Only a few studies have reported the rheological properties of caprine milk cheese (Attaie and others 1996), and even fewer examine the rela- tionship between proteolysis and rheology (Van Hekken and others 2004; Attaie 2005). A joint study was developed to understand the complex fac- tors that contribute to the quality of caprine milk cheese. Exam- ination of weekly milk composition showed typical changes in milk composition as the lactation progressed (Fekadu and oth- ers 2005). When cheeses manufactured early (weeks 4 and 5), midway (weeks 12, 14, and 15), and late (weeks 21, 22, and 23) in the lactation cycle were examined, the composition of the cheeses was fairly stable between weeks 5 and 22 (Olson and others 2007). Examination of the functional properties of cheese made at the 3 different periods of lactation showed that meltabil- ity, sliceability, and color change upon heating were affected by the week of lactation that the milk was obtained and by aging of the cheese at 4 ◦ C (Olson and others 2006). This paper also exami- ned the cheeses made at 3 different periods of lactation and reports on the effects of aging on the proteolytic and rheological properties of cheddar-like caprine milk cheeses. No claim to original US government works C  2007 Institute of Food Technologists Vol. 72, Nr. 3, 2007—JOURNAL OF FOOD SCIENCE E115 doi: 10.1111/j.1750-3841.2007.00296.x Further reproduction without permission is prohibited