JFS: Food Chemistry and Toxicology Moisture Loss and Lipid Oxidation for Precooked Beef Patties Stored in Edible Coatings and Films Y. WU, J.W. RHIM, C.L. WELLER, F. HAMOUZ, S. CUPPETT, AND M. SCHNEPF Food Chemistry and Toxicology ABSTRACT: Edible/biodegradable wheat gluten (WG), soy protein (SP), carrageenan (CA) and chitosan (CH) films and coatings were used on precooked beef patties. After 3 d of refrigerated storage, no difference was found in moisture loss between WG, SP, and CH film-wrapped patties and unpackaged patties (control-A). All coatings were as effective as polyvinyl chloride film (control-B) in reducing moisture loss. CA film decreased moisture loss but not as effective as control-B. WG, SP, and CA coatings and CA film reduced thiobarbituric acid-reactive substances and hexanal values compared to control-A. WG-coated patties had lower hexanal values than control-B samples. WG, SP, and CH films were not effective in controlling lipid oxidation. Key Words: edible/biodegradable coatings, edible/biodegradable films, precooked beef patties, moisture loss, lipid oxidation Introduction P RECOOKED MEAT PRODUCTS ARE SUSCEPTIBLE TO LIPID OXI- dation, which leads to rapid development of rancid or stale flavor, denoted as warmed-over flavor (WOF), during refrigerated storage (Tims and Watts 1958; St. Angelo and Bailey 1987; Love 1988). Moisture loss is a critical factor affecting the quality and shelf life of precooked meats. As consumer demand for more convenience food has grown rapidly (Hollingsworth 1994), much effort has been devoted to improving quality of precooked meat products. Among many techniques used to control the quality of precooked meats, appropriate packaging is a common solution for maintaining precooked meat quality. Edible/biodegradable coatings and films produced from polysaccharides, proteins, and/or wax and lipid derivatives can function as efficient barriers to moisture and/or oxygen. Edible barriers are environment-friendly without the negative effects caused by nonrenewable food packaging materials (Guilbert and others 1996; Debeaufort and others 1998; Krochta and De Mulder-Jonston 1997). Therefore, they may represent methods of alternative packaging that can be used to maintain the quality and prolong the shelf life of foods. Various types of coatings and films have been tested in an attempt to maintain the quality of meat products, including fresh beef and pork (Allen and others 1963; Williams and others 1978); lamb (Lazarus and others 1976); poultry (Meyer and others 1959; Allen and others 1963); and also frozen products, such as beef (Rice 1994), pork (Wanstedt and others 1981), and fish (Stuchell and Krochta 1995; Hwang and others 1997). However, the application of edible/biodegradable coatings and films on precooked meat products has not been as extensively studied as has their applications on fresh and frozen meat products (Gennadios and others 1997). Wanstedt and others (1981) reported that alginate-coated precooked, frozen stored pork patties had improved sensory qualities and were more desirable than control patties. Lipid oxidation was inhibited and WOF was eliminated in the coated patties. Coatings of starch-alginate, starch-alginate-tocopherol, and starch-alginaterosemary have been shown to reduce effectively WOF in precooked, refrigerated pork chops and beef patties (Hargens-Madsen and others 1995; Ma-Edmonds and others 1995; Handley and others 1996). Lipid oxidation and WOF formation were also 300 JOURNAL OF FOOD SCIENCE—Vol. 65, No. 2, 2000 controlled by corn zein and corn zein-tocopherol coatings in precooked, refrigerated pork chops (Hargens-Madsen and others 1995). Pork chops and beef patties in these studies were juicier than uncoated control samples as judged by sensory scores. Herald and others (1996) wrapped precooked turkey breast slices in corn zein films containing butylated hydroxyanisole (BHA) and reported that turkey breast wrapped in corn zein films had less WOF than samples packaged in polyvinylidene chloride (PVDC) plastic wrap. However, edible coatings of 7S soy protein were not found to be as effective as phosphate in retarding the formation of WOF in precooked chicken breast (Kunte 1996). This study was conducted with the objective of evaluating the effectiveness of coatings and films made with wheat gluten (WG), soy protein (SP), carrageenan (CA), and chitosan (CH) against moisture loss and lipid oxidation in precooked ground beef patties. Results and Discussion Apparent characteristics of coatings and films Coatings and films made from two types of polysaccharides and two types of protein were used in this study. Table 1 shows the apparent characteristics of these coatings and films on precooked beef patties at the beginning of storage and after storage. Changes in apparent characteristics of these coatings and films after use on beef patties and being stored for 3 d at 4 ⬚C were associated with their barrier properties as discussed below. Relative moisture loss After 3 d of storage at 4 ⬚C, there was a significant treatment effect in relative moisture loss (RML) (%) of beef patties (Fig. 1). Unpackaged control-A patties exhibited the highest RML and became dry on the surface (visual observation). Significant reduction of RML by 79%, 57%, 61%, 92%, and 66% over control-A was observed in polyvinyl chloride (PVC) -packaged patties (control-B), WG, SP, CA and CH-coated patties, respectively. All coated patties had similar RML to that of control-B patties, and no visual dryness was observed in these patties. PVC is known to be effective in retarding the passage of water vapor (Brody 1997) and widely used in food service systems (Doshi 1997). The effect © 2000 Institute of Food Technologists Fig. 1—Relative moisture loss of precooked beef patties not packaged (A), packaged in polyvinyl chloride (B), and packaged in edible/ biodegradable coatings and films of wheat gluten (WG), soy protein (SP), carrageenan (CA) or chitosan (CH) after 3 d of storage at 4 oC. Letters a through e indicate relative moisture loss means are significantly different (p < 0.05). Table 1—Apparent characteristics of coatings and films of wheat gluten (WG), soy protein (SP), carrageenan (CA) and chitosan (CH) on precooked beef patties at the beginning and after 3-d storage Coatings/films WG-coatings SP-coatings CA-coatings CH-coatings WG-film SP-film CA-film CH-film Appearance on patties at the beginning of storage Appearance on patties after 3-d storage sticky gel sticky gel solidified clear gel solidified clear gel translucent dry film transparent dry film transparent dry film transparent dry film visible film invisible film visible gel-like film invisible film swelled gel swelled gel not swelled, transparent film swelled gel and wrapping treatments and between protein and polysaccharide treatments was compared with contrast tests. In general, coatings were significantly more effective in preventing moisture loss than wrappings, while protein materials were less (p ⬍ 0.05) effective than polysaccharide materials. This may be attributed to the different moisture transfer behaviors of the coatings and films discussed above. Values of TBA-reactive substances The 2-thiobarbituric acid (TBA) test has been widely used to estimate the extent of lipid oxidation in meat and meat products (Shahidi 1994). Thiobarbituric acid-reactive substances (TBARS) of patties in control-A, control-B, and patties coated or wrapped with CA, CH, WG, and SP were determined and compared as shown in Fig. 2. TBARS of PVC- wrapped patties (control-B) were 23% lower (p ⬍ 0.05) than those of control-A. This may be due to the good O2 barrier properties of PVC (Paine and Paine 1992). Different film and coating treatments in our study showed different effects in TBARS. Coating with WG, SP, or CA and wrapping with CA was as effective (p ⬍ 0.05) as wrapping with PVC in reducing TBARS, while the TBARS in WG- coated samples were the lowest. This suggests that the oxidation of precooked beef patties may be controlled to some extent with these treatments. Among the treatments tested, coating with WG may be the most effective method in controlling lipid oxidation. WG-based films are known to be good O2 barriers. Their potential use as packaging materials for perishable foods has been suggested (Gennadios and others 1993; Herald and others 1995; Park and Chinnan 1995). Reportedly, WG coatings have been applied on eggs (Herald and others 1995) and resulted in Grade A quality shell eggs maintaining quality for 30 d at room temperature. The WG coating used in our study became a visible integral film after storage (Table 1), which may contribute to its barrier properties. Soy protein films have also been found to be very effective O2 barriers (Brandenburg and others 1993). The antioxidant activity contained in soy protein preparations has been well established (Bowers and Engler 1975; Romijn and others 1991). Incrementally adding either a textured soy protein (Bowers and Engler 1975) or SP (Romijn and others 1991) into ground beef produced progressive decreases in TBA values in the cooked beef systems. Similarly, when Kunte (1996) tumbled 7S soy protein with raw chicken breast, less lipid oxidation and less WOF in the cooked chicken were detected. In the same study, however, edible coatings of 7S soy protein did not retard the formation of WOF in precooked chicken breast. The different types of soy protein, food products, and techniques for film formation used in these studies may account for the discrepancies noted between our data and those in the literature. Although carrageenan coatings or films have not been used on cooked meats, carrageenan films have been successfully used to inhibit the oxidation of fresh mackerel mince patties as measured by peroxide values and TBA Vol. 65, No. 2, 2000—JOURNAL OF FOOD SCIENCE 301 Food Chemistry and Toxicology of coatings on RML, especially CA and CH coatings, which were in the form of high-moisture gelatinous coatings (Table 1), may be due to their function as moisture-sacrificing agents instead of moisture barriers, that is, the coatings gave up their moisture prior to any significant desiccation of the packaged food products (Kester and Fennema 1986). Thus, the loss of product moisture could be delayed until the moisture contained within the gel had been evaporated. CH coatings have been shown to reduce water loss and prolong the storage life of fruits and vegetables (El Ghaouth and others 1991a, 1991b). Alginate coatings have been reported to be effective in reducing moisture loss and improving the juiciness of fresh beef steak, pork chops, skinned chicken drumstick meat (Allen and others 1963), and lamb carcasses (Lazarus and others 1976). Precooked pork chops and ground beef patties coated with starch-alginate were juicier than uncoated samples as judged by the sensory scores (Hargens-Madsen and others 1995; Ma-Edmonds and others 1995). As shown in Fig. 1, CH, WG, and SP film wrappings did not lower RML in patties when compared with control-A. Patties wrapped with these films had higher (p ⬍ 0.05) RML than those with coatings and the control-B patties and became dry on the surface during the storage. Due to their hydrophilic nature, films primarily composed of polysaccharides or proteins are highly sensitive to moisture and show poor water vapor barrier properties (Guilbert 1986; Krochta 1992; Gennadios and others 1994; Guilbert and others 1996). All film wrappings in this study, except CA film, absorbed water and slowly swelled (Table 1). Film swelling is believed to be due to the conformational changes involving structural relaxation (Slade and others 1989). These may have contributed to the observed higher RML in those wrapped samples. Interestingly, CA film did not absorb water and swell when applied to beef patties. Though they were not as effective as PVC packaging, and dryness was also observed on the surface of CAfilm-wrapped patties, CA films lowered the RML in patties with a 41% reduction over control-A. In a study conducted by Hwang and others (1997), swelling of CA films was not noted when being used on mackerel mince patties, and the film did not show any ability to reduce moisture loss. Water vapor transfers through hydrophilic films by sorption and diffusion and is affected by many factors (McHugh and Krochta 1994; Wagner 1997). Therefore, the mechanism involved in the water vapor transfer through the CA films may need to be studied further. The effectiveness in reducing moisture loss between coating Protein and Polysaccharide Coatings/Films for Precooked Meat . . . Food Chemistry and Toxicology values (Hwang and others 1997). Coating with CH or wrapping with CH, WG, or SP did not significantly reduce TBARS when compared with control-A. All these treatments had higher (p ⬍ 0.05) TBARS than control-B. No significant differences were found among these treatments. A higher O2 permeability may contribute to the higher TBARS from these treatments. After being applied on patties and during the 3 d of storage, the CH, WG, and SP wrappings absorbed moisture from meat samples and swelled (Table 1). The plasticizing effect of water molecules may have changed the barrier properties of the edible films (Gontard and others 1996; Krochta 1997) and resulted in higher O2 permeability and even loss of film integrity. The composition of the CH film might also contribute to its higher O2 permeability. Chitosan is water-insoluble but is readily soluble in dilute organic acid (Rodriguez-Sanchez and Rha 1981). Formic acid was used as solvent to form CH film in our study. Formic CH film has been reported to have higher O2 permeating coefficient than lactic acid and acetic acid CH films (Caner and others 1998) but was more resistant against water than other acid CH films (Rhim and others 1998b). Acetic acid has often been the solvent for the production of CH films (Hosokawa and others 1990; Butler and others 1996) but acetic acid CH film has a strong vinegar flavor, which probably would prevent them from being used in edible films (Rhim and others 1998b). With their gas semipermeable properties (Nisperos-Carriedo 1994), CH coatings have been reported to be effective in retarding and prolonging storage life of tomatoes, cucumbers, bell pepper fruits, and fresh strawberries without affecting their ripening characteristics (El Ghaouth and others 1991a, 1991b). CH by itself has been shown to have chelator antioxidant activity in cooked ground beef to inhibit WOF when mixed with the meat samples (St. Angelo and others 1988). However, they were not effective, as shown in our study, when they were applied on the meat surface as coatings or films. Generally, coatings may be more (p ⬍ 0.0511) effective in reducing TBARS than wrappings in the present study. Edible coatings of alginate (Wanstedt and others 1981) and starch-alginate (Hargens-Madsen and others 1995; Ma-Edmonds and others 1995; Handley and others 1996) were reported to be effective in reducing TBA values or TBARS in precooked frozen stored pork patties (Wanstedt and others 1981), precooked, refrigerated stored pork chops (Hargens-Madsen and others 1995; Handley and others 1996) and beef patties (Ma-Edmonds and others 1995). Corn zein coatings also resulted in lower TBARS for precooked pork chops than uncoated control after 6 and 9 d of refrigerated storage (Hargens-Madsen and others 1995). Moreover, there was a trend showing a significant (p ⬍ 0.0609) difference in TBARS between protein treatments and polysaccharide treatments in our study, implying that protein treatments may be more effective in reducing TBARS than those of polysaccharides. This may be attributed to the better O2 barrier properties of protein films, in general (Krochta 1997). Fig. 2—Values of thiobarbituric acid reactive-substances (TBARS) of precooked beef patties not packaged (A), packaged in polyvinyl chloride (B), and packaged in edible/biodegradable coatings and films of wheat gluten (WG), soy protein (SP), carrageenan (CA) or chitosan (CH) after 3 d of storage at 4 oC. Letters a through e indicate relative moisture loss means are significantly different (p < 0.05). Fig. 3—Hexanal values of precooked beef patties not packaged (A), packaged in polyvinyl chloride (B), and packaged in edible/biodegradable coatings and films of wheat gluten (WG), soy protein (SP), carrageenan (CA) or chitosan (CH) after 3 d of storage at 4 oC. Letters a through e indicate relative moisture loss means are significantly different (p < 0.05). 302 JOURNAL OF FOOD SCIENCE—Vol. 65, No. 2, 2000 Hexanal value Hexanal has been shown to be one of the dominant volatile products of oxidized lipid that contributes to the WOF (Shahidi and others 1987; St. Angelo and others 1987; Shahidi 1994). The hexanal value of all treatments was varied depending on the type of packaging used in the present study (Fig. 3). Similar to those results for TBARS, coating with CH, and wrapping with CH, WG, or SP did not significantly reduce hexanal values when compared with control-A, which had the highest hexanal value. No significant differences were found between CH, WG, and SP wrapping treatments. However, coating with WG, SP, or CA and wrapping with CA significantly decreased hexanal values in the patties. Among these four treatments, CA and SP coating and CA wrapping resulted in similar hexanal values as the PVC packaging, while CA wrapping gave rise to a higher (p ⬍ 0.05) hexanal value than PVC . The hexanal value of the WG-coated patties was even lower (p ⬍ 0.05) than that of the PVC-wrapped patties, suggesting WG coating may be more effective in controlling lipid oxidation and WOF than the plastic PVC. The effectiveness of edible films and coatings in inhibiting the formation of hexanal and the development of WOF in precooked meats has been reported when applying starch-alginate coatings on pork chops (Handley and others 1996) or beef patties (Ma-Edmonds and others 1995) and using corn zein films with butylated hydroxytoluene (BHT) to wrap turkey breast (Herald and others 1996). The corn zein films used in the study of Herald and others (1996) were demonstrated to be even more effective than polyvinylidene chloride wrapping in reducing the formation of hexanal. However, films without BHT were not tested in their study. Results from our study showed that coatings, in general, were significantly more effective than films in retarding the formation of hexanal. There was also a trend showing that protein films may be better O2 barriers than polysaccharide films. The average hexanal values of Conclusions C OATINGS WERE MORE EFFECTIVE IN CONTROLLING RML THAN wrappings. Coating with WG, CA, or SP and wrapping with Materials and Methods Materials The following materials were used: wheat gluten, (DO-PEP; ADM Arkady, Olathe, Kans., U.S.A.); soy protein isolate (Supro 620; Protein Technologies International, St. Louis, Mo., U.S.A.); chitosan (minimum 85% deacetylated; Sigma Chemical Co., St. Louis, Mo., U.S.A.); -carrageenan (Hankook Carrageen Industrial Company, Soonchun, Chonnam, Korea); ammonium hydroxide, formic acid, glycerin, and sodium hydroxide (J.T. Baker Inc., Phillipsburg, N.J., U.S.A.); ethyl alcohol (USP 95% to 190% proof; McCormick Distilling Co. Inc., Weston, Mo., U.S.A.); thiobarbituric acid, butylated hydroxytoluene (BHT), and hexanal (Sigma Chemical Co., St. Louis, Mo., U.S.A.); potassium chloride (Fisher Scientific, Pittsburgh, Pa., U.S.A.); and polyvinyl chloride (PVC) food wrap film (Nugget Distributors Inc. Stockton, Calif., U.S.A.). Preparation of coatings and films WG film-forming solutions were prepared using the formula of Gennadios and others (1993). WG (10 g) was dispersed in a solution of 95% ethanol (48 mL) and glycerin (4 g) by heating and stirring on a magnetic stirrer/hot plate and slowly adding 32 mL distilled water and 8 mL of 6N ammonium hydroxide. The end point of the dispersion was visually determined by a significant decrease in solution viscosity when the temperature of the solution was 75 to 77 ⬚C. Films prepared using this method had a thickness of 0.078 to 0.124 mm and a WVP value of 4.57 to 5.09 g mm/m2 d KPa (Gennadios and others 1993). Using the method of Rhim and others (1998a), an SP filmforming solution was prepared by slowly dissolving 5 g protein in a constantly stirred mixture of distilled water (100 mL) and glycerin (2.5 g). The pH of the solution was adjusted to 10⫾0.1 with 1N sodium hydroxide. Subsequently, the solution was heated for 20 min in a constant temperature water bath at 80 ⬚C. Films prepared using this method had a thickness of 0.061 to 0.065 mm and a WVP value of 2.07 to 2.17 g mm/m2 d KPa (Rhim and others 1998a). A CH film-forming mixture was prepared by dissolving 3 g CH in 150 mL of 1% formic acid with 0.75 g glycerin, using the method of Rhim and others (1998b). The mixture was heated to boiling (about 100 ⬚C) on a magnetic stirrer/hot plate until the solution became clear. Films prepared using this method had a thickness of 0.047 to 0.059 mm and a WVP value of 144.64 to 167.28 g mm/m2 d KPa (Rhim and others 1998b). -Carrageenan (3 g) and potassium chloride (0. 15 g) were slowly dissolved in a mixture of distilled water (150 mL) and glycerin (0.75 g) to prepare a CA film-forming solution (Rhim and others 1996). The solution was then heated to boiling (about 100 ⬚C) to dissolve the components on a magnetic stirrer/hot plate until clear. Films prepared using this method had a thickness of 0.050 to 0.11 mm and a WVP value of 22.03 to 38.33 g mm/m2 d KPa (Rhim and others 1996). Film solutions were strained through 8-layer cheese cloth (grade 40; Fisher Scientific, Pittsburgh, Pa., U.S.A.) to remove foam and undissolved materials. To prepare films for wrapping, all prepared film-forming solutions were cast, while still CA was effective in controlling lipid oxidation, with WG coating being the most effective. These coatings and films afford potentials as oxygen barriers for precooked meat products. Further research needs to be conducted on edible/biodegradable films to improve moisture barrier properties and the application of such films on food products. warm, on Teflon-coated glass plates (21 cm ⫻ 35 cm), except WG film, which was cast on a clean, flat glass surface. For casting WG film, a thin-layer chromatography spreader bar (Brinkman Co., New York, N.Y., U.S.A.) was filled each time with the solution and moved along the glass plate to distribute the solution as evenly as possible. Cast solutions were allowed to dry at room conditions overnight, peeled off the plates, and readied for application on meat samples. Coating solutions were prepared using the same formulas as the corresponding film-forming solutions. The total volume of each coating solution used for coating was 300 mL. Meat sample preparation and packaging application Fresh ground beef patties (80% lean), obtained from a local supermarket, were grilled on each side for approximately 4 min on a flat Hobart griddle (Model HG-4; Troy, Ohio, U.S.A.) at 171 ⬚C to an internal temperature of 71 ⬚C. Cooked patties were immediately frozen until packaged within 24 h. The patties were either dipped in the coating solutions or wrapped with films and immediately refrigerated at 4 ⬚C for 3 d. For coating patties, skewers were used to hold patties and completely immerse each patty into a coating solution for 10 s. Each patty was drained for 10 s, then dried for 2 min in front of a small electric fan. Patties without coating/wrapping or wrapped with PVC food wrap film were used as control-A and control-B, respectively. Apparent characteristics of coatings and films Appearances of coatings and films on precooked beef patties were visually evaluated at the beginning of storage and after storage for 3 d at 4 ⬚C. Relative moisture loss (RML) Moisture content of samples was determined using AOAC standard method 950.46 (AOAC, 1990). Duplicate 2-g samples were oven-dried at 102 ⬚C for 18 h. Samples were then cooled in a desiccator to room temperature and reweighed. Moisture content was determined on cooked samples before and after storage for 3 d at 4 ⬚C. RML was calculated as: RML (%) ⫽ [(initial MC ⫺ final MC)/initial MC] ⫻ 100 2-Thiobarbituric acid (TBA) test The TBA test was conducted on day 3 of refrigerated storage using the method of Tarladgis and others (1960) as modified by Pikul and others (1984). BHT was added during sample preparation. Malondialdehyde (MDA) and other aldehydes in the precooked beef patties were measured and reported as values of thiobarbituric acid-reactive substances (TBARS) in units of MDA/kg sample. Duplicate 10-g samples were analyzed. Headspace gas chromatographic (HS-GC) analysis An analysis of volatiles was performed using the HS-GC method developed by Handley and others (1996) and modified by Wu and others (1998) with a Tekmar 7000 headspace autosampler (Cincinnati, Ohio, U.S.A.) attached to a Hewlett Packard gas chromatograph (Model 5890; Avondale, Pa., Vol. 65, No. 2, 2000—JOURNAL OF FOOD SCIENCE 303 Food Chemistry and Toxicology protein treatments were significantly lower than that of polysaccharide treatments. Protein and Polysaccharide Coatings/Films for Precooked Meat . . . U.S.A.) equipped with a fused silica capillary column (30 m ⫻ 0.320 mm inner diameter, 1.00 µm film, DB-5; J & W Co., Folsom, Calif., U.S.A.) and a flame ionization detector. Triplicate 6-g samples were analyzed. The sample was sealed in a 22mL glass headspace vial with a sample phase fraction of 0.5 and equilibrated at a platen temperature of 120 ⬚C for 15 min in the headspace autosampler. 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Food Sci. 43:292-296. Wu Y, Hamouz F, Schnepf M. 1998. Factors affecting static headspace-gas chromatographic analysis of lipid oxidation in precooked meat. J. Agric. Food Chem. 46:3677-3682. This paper was published as Journal Series No. 12672, Agricultural Research Division, Institute of Agriculture and Natural Resources, University of Nebraska-Lincoln. It was presented at the 1999 Annual Meeting of the IFT in Chicago, Ill. Authors Wu, Hamouz, and Schnepf are affiliated with the Dept. of Nutritional Science and Dietetics, Univ. of Nebraska-Lincoln, Lincoln, NE 685830806. Author Rhim is with the Dept. of Food Engineering, Mokpo National Univ., Chonnam, 534-729, Republic of Korea. Author Weller is with the Industrial Agricultural Products Center and Department of Biological/Systems Engineering, Univ. of Nebraska-Lincoln, Lincoln, NE 68583-0730. Author Cuppett is with the Dept. of Food Science and Technology, Univ. of NebraskaLincoln, Lincoln, NE 68583-0919. Direct inquiries to author Schnepf (E-mail: [email protected]).
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