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Document Type

Thesis - University Access Only

Award Date

1997

Degree Name

Master of Science (MS)

Department

Dairy Science

First Advisor

Vikram V. Mistry

Abstract

The objective of this study was to study the effect of ultrafiltered sweet buttermilk (UBM), sweet buttermilk powder (BMP) and nonfat dry milk (NDM) on chemical, physical, sensory, microstructural and microbiological properties of nonfat and lowfat yogurts. Experiments included five replications consisting of three ingredients (UBM, BMP and NDM) and two fat levels (0.34% and 1.36%). Ultrafiltered sweet buttermilk (13.77% protein), BMP (31.45% protein) or NDM (36.2% protein) were used to fortify skim milk to 3.65 to 3.77% protein and 9.55 to 10.39% total solids (TS) in nonfat yogurt (NF) mix, and 4.40 to 6.39% protein and 13.4% TS in lowfat yogurt (LF) mix. Fat was adjusted with 40% fat cream to 0.34% in NF and 1.36% in LF. Mixes were homogenized at 20 MPa, pasteurized at 82.2°C for 30 min, inoculated with a mixed yogurt culture, incubated at 43°C for 4.5 hand cooled to 4°C. Titratable acidity (TA) of LF yogurts was higher (P0.05) TA of yogurts at any time period. As storage time increased, the TA increased pH of lowfat yogurts was higher (P < 0.05) than that of nonfat yogurts. There were no differences (P > 0.05) in, TA and pH among nonfat yogurts. Lowfat yogurt with UBM had the highest (P< 0.05) pH and TA suggesting increased buffer capacity. Lowfat yogurt with UBM was the firmest (P< 0.05); whereas BMP-LF was softer (P < 0.05) than NDM-LF. Treatment did not affect firmness of nonfat yogurts. As speed of shearing increased, viscosity of yogurts decreased indicating shear thinning property and at high speed of shearing, time of shearing had little effect on yogurt viscosity. Viscosity of UBM-LF was the highest (P < 0.05). Nonfat yogurts with UBM and BMP were similar in flavor, appearance, texture, aroma, smoothness and sourness to NDM-NF. Lowfat yogurt with UBM received the lowest (P < 0.05) flavor score and sourness, but the highest (P < 0.05) appearance score. Overall acceptability for BMP-LF was similar (P > 0.05) to NDM-LF, but BMP-LF was smoother (P < 0.05). Two-wk-old UBM-LF was the least acidic. Although rods to cocci ratio of yogurt was approximately 1:4, yogurts with good flavor were obtained. Microstructures of nonfat yogurts were more open than those of lowfat yogurts, possibly due to higher protein contents of the latter. Ultrafiltered sweet buttermilk yielded the densest matrix with fused casein particles. It is likely that whey protein denaturation was responsible for this phenomenon. Addition of BMP to yogurt mix up to 4.8% yielded soft and smooth product.

Library of Congress Subject Headings

Yogurt
Buttermilk
Food -- Fat content

Description

Includes bibliographical references (pages 38-46)

Format

application/pdf

Number of Pages

80

Publisher

South Dakota State University

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