652—JOURNAL OF FOOD SCIENCE—Volume 61, No. 3, 1996 Morphology and Texture of Bologna Sausage as Related to Content of Fat, Starch and Egg White J. CARBALLO, P. FERNANDEZ, G. BARRETO, M.T. SOLAS, and F. JIMENEZ COLMENERO Table 1—Levels of variables in bologna sausage formulations Samples Fat (%) Starch (%) Egg white (%) 7/5/1.5 20/5/1.5 7.0 20.0 5.0 5.0 1.5 1.5 14/0/1.5 14/10/1.5 14.0 14.0 0 10.0 1.5 1.5 14/5/0 14/5/3 14.0 14.0 5.0 5.0 0 3.0 14/5/1.5 14.0 5.0 1.5 ABSTRACT The effects of fat (7.0, 14.0 and 20.0%), starch (0, 5 and 10%) and egg white (0, 1.5 and 3%) on the microstructure and texture of bologna sausages were examined. As levels of fat and starch increased, the mi- crostructure exhibited increasing numbers of holes (P0.05), smaller in size (P0.05) and similar (P0.05) in shape. No clear relationship was found between addition of egg white and these morphological variations. Low-fat sausage (7.0%) was less hard and chewy (P0.05) than high- fat (20.0%) sausage; likewise, a direct relationship was found between starch and egg white content and hardness and chewiness of the bologna. Key Words: fat content, starch, egg white, microstructure, meat emul- sion. INTRODUCTION THE INFLUENCE OF FAT on texture causes difficulties in the prep- aration of low-fat meat emulsion products (Hand et al., 1987; Claus et al., 1989, 1990; Cavestany et al., 1994). In order to offset the effects of reduced fat levels and obtain acceptable products, a variety of technological procedures have been tried (Hand et al., 1987; Claus et al., 1989; Bishop et al., 1993; Gregg et al., 1993). Also addition of a variety of non-meat ingredients has been studied (Shand et al., 1990; Claus and Hunt, 1991; Keeton, 1992; Troy, 1993). Among such ingredients of potential use are starch (Claus and Hunt, 1991; Hull et al., 1992; Dexter et al., 1993; Carballo et al., 1995) and egg white (Troy, 1993; Carballo et al., 1995). Combinations of starches and/or proteins appear to provide a useful means of replacing a notable portion of fat in meat prod- ucts (Keeton, 1992). Both modified waxy corn starch and egg white affect texture of bologna sausage with different fat levels, but to differing degrees (Carballo et al., 1995). This has been attributed essentially to the effects that the ingredients exert upon the structural characteristics of the protein gel matrix (Niwa, 1992; Chen et al., 1993; Carballo et al., 1995). However, very little has been done to establish relationships between mi- crostructural and textural characteristics of meat emulsions in relation to composition variables. The objective of this research was to analyze the relationship between microstructural and textural characteristics of meat emulsions with reference to fat content and levels of added starch and egg white. MATERIALS & METHODS RAW MATERIALS and preparation of bologna sausages were as described by Carballo et al. (1995). Pork meat and fat trim (perirenal/peritoneal), water, starch and egg white were combined to give levels of each vari- able established for every formulation (Table 1). Meat protein content was adjusted to 12.5% in all formulations. The starch (Clearan CH 20, Roquette Fre `res, Lestrem, France) was a waxy corn starch modified to maintain functional behavior at pasteurizing and freezing temperatures. Authors Carballo, Fernandez, Barreto, and Jimenez Colmenero are affiliated with Instituto del Frio (CSIC), Ciudad Universitaria 28040, Madrid, Spain. Author Solas is with the Dept. of Cellular Biology, Biology Faculty, Universidad Complutense, 28040 Ma- drid, Spain. Atomized dried egg white (EW) (Sanofi, S.A., Barcelona, Spain) was used. As established in the experimental design, the 14/5/1.5 sample represented the mid-point of ranges studied for the variables fat, starch and egg white (Table 1). Moisture, protein and ash of bologna sausage were determined in trip- licate by the AOAC (1984) method. Fat was evaluated by difference. Microstructure was examined by scanning electron microscopy (SEM) following the procedure described by Cavestany et al. (1994). Samples were fixed in 2% glutaraldehyde in 0.1M phosphate buffer pH 7.2, post- fixed with OsO 4 , washed, dehydrated in increasing series of acetone, critical-point dried, sputter-coated with gold/palladium and scanned by SEM at 20 kV (Jeol JSM 6400, Akishima, Tokyo, Japan). The following morphological parameters were quantified: number of holes or cavities (NH) in 1000 μ 2 of sample, average area of holes (SH, μ 2 ); elipticity, expressed as D max /D min of the holes, and surface of matrix (SM, μ 2 of zone without holes, total area - area of holes) in 1000 μ 2 of sample. These microstructural characteristics were quantified densitometrically using VIDEOPLAN, Software Release 2.1, Kontron Bildanalyse GmbH. Results are average evaluations of 4 different micrographs for each sam- ple. Texture profile analysis (TPA) was performed in a Universal Testing Machine (Model 4501 Instron Engineering Corp., Canton, MA) as de- scribed by Carballo et al. (1995). Five bologna cores (diam 2.5 cm, height 2.0 cm) per treatment were axially compressed to 50% of their original height. Force-time deformation curves were derived with a 5 kN load cell applied at a crosshead speed of 50 mm/min. Attributes were calculated on the basis of: hardness (Hd) = peak force (N) required for first compression; cohesiveness (Ch) = ratio of active work done under the second compression curve to that done under the first compression curve (dimensionless); springiness (Sp) = distance (mm) the sample re- covers after the first compression; chewiness (Cw) = Hd  Ch  Sp (N  m). Analysis of variance with an F test, and least squares differences, were used to compare means and to identify significant differences (P0.05) among treatments. Coefficients of correlation (r) between texture and morphological parameters were calculated. Data analyses were per- formed using the Statgraphics 5.0 program. RESULTS & DISCUSSION OVERALL MEAN VALUES of the three levels of fat content in the samples formulated were 7.2%, 13.9%, and 20.1%, close to tar- get levels (Table 1). Percentages of moisture ranged from 57.6% to 69.8% and ash 3.0% to 3.4%, depending on level of variables concerned. Protein levels ranged from 12.7% to 15.5%, but since meat protein was held constant at 12.5%, the increase in overall protein content was the result of adding egg protein. However, minor variations found in actual as opposed to target proximate composition may be ascribed partly to two causes. Slight errors could occur in product preparation process, causing slight divergence from planned composition. Alterations to sau-