Investigation of Sustainability of Dairy Goat Industry by Innovative Method of Product Development

Investigation of Sustainability of Dairy Goat Industry by Innovative Method of Product Development

Summary

Effects of refrigerated and frozen storage on shelf-life of commercial soft goat milk cheeses were evaluated in relation to microbiological, physico-chemical, and rheological characteristics. Although some variations were observed between lots of the cheeses, coliforms and E. coli counts were non-detectable, while non-coliforms such as Pseudomonas were present. No Staphylococcus aureus were detected, whereas unidentified presumptive Staphylococcus species may exist. Cohesiveness of the cheeses significantly decreased, while viscoelastic properties remained unchanged as storage progressed. Yeast and mold counts were inversely correlated with cohesiveness. Greater increases in lipolytic and proteolytic parameters such as water soluble N and acid degree values occurred in frozen-stored cheeses than fresh ones, which needs further investigation.

Objectives/Performance Targets

1. Evaluate food quality and shelf-life of the commercial fresh soft goat milk cheeses produced by the Georgia dairy goat farmers.

   Compare the same parameters of the frozen-stored soft goat milk cheeses after 3 to 6 months at –20oC with those of the fresh cheeses for off-season marketing.

   Determine microbiological, rheological, nutritional and physico-chemical changes in fresh and frozen-stored soft goat cheeses in relation to the shelf-life and storage quality of the products.

Accomplishments/Milestones

Because of the problem of delaying in hiring a Research Associate for the project, its period has been requested to extend at least one more year. For the first year of the project, active research has been initiated on evaluation of storage quality of soft goat milk cheeses. Instead of using the hard goat cheeses developed at Fort Valley State University dairy plant as originally planned, commercial soft goat milk cheeses manufactured by a licensed farmstead goat dairy in Georgia were evaluated for shelf-life and storage stability of refrigerated and frozen stored goat cheeses, as recommended by the project evaluating committee. The results of this part of investigation will provide consumers and producers with more practical knowledge and information on the shelf-life and storage quality of the currently marketed goat cheeses in real world.

The soft goat cheeses were purchased from the Grade A goat dairy, and stored at 4oC for 0, 7, 14, and 21 days. Microbiological assays for total aerobic, E. coli and coliform, yeast and mold, and Staphylococcus aureus counts were performed using 3M petrifilm plates techniques according to the manufacturer’s recommended procedures. Rheological parameters were determined using a universal testing machine and a small strain oscillatory analyzer. Total aerobic counts of the soft goat cheeses were too numerous to count (TNTC) regardless of treatments and lengths of storage periods, probably due to the lactobacilli counts. The respective ranges of yeast and mold counts were 104 –106cells/g and 103-104 cells/g cheese, and both counts were increased with storage time. Coliforms, E. coli and S. aureus were not detectable, while non-coliform organisms such as Pseudomonas and many unidentified presumptive Staphylococcus species appeared to be present. Rheological properties revealed that cohesiveness of the soft goat cheeses significantly decreased, while viscoelastic properties remained unchanged as aging time progressed. An inverse correlation occurred between the yeast and mold counts and cohesiveness of the tested cheeses. The significant deterioration in shelf-life of the cheese at 21 days storage may be attributed to the elevated Pseudomonas, yeast and mold counts, which might have accelerated lipolytic and proteolytic processes in the stored products.

In assessing the shelf-life of fresh and frozen cheeses in relation to proteolytic and lipolytic parameters, one batch of the soft cheeses was frozen, stored for 3 months, thawed, and compared for the differences between the fresh and frozen-stored products. Total N, % water soluble N (WSN), pH and acid degree values (ADV) were determined, and protein profiles of fresh cheeses were examined using SDS-PAGE and densitometric analysis. The %WSN ranged from 4.4 to 11, and increased with storage time with the concomitant decrease in beta-casein as revealed in the SDS-PAGE and densitometric results. A greater increase in WSN occurred in frozen-stored cheeses than the fresh ones, suggesting that frozen-storage and thawing might have accelerated protein degradation in the frozen thawed cheeses, presumably due to the denaturation of cheese proteins as well as activation of some proteinase enzymes. ADVs were significantly increased with storage period, and were higher in frozen-stored than fresh cheeses.

For the subsequent years of this project, we intend to perform further comprehensive studies on the evaluation of soft goat cheeses in along with one or two developed hard type goat cheeses. The pursued objectives are: (1) Develop semi-hard and hard (Monterey Jack and Cheddar-type) goat milk cheeses using the surplus milk during the peak season, and store the cheeses at 4oC and –20oC for 0, 3, and 6 moths; (2) Study the effects of freezing and storage on food quality and shelf-life of the experimental soft and hard goat cheeses in rheological, nutritional, microbiological, physico-chemical and flavor chemical characteristics of the products; (3) Conduct sensory evaluation and consumer acceptability studies on the soft and developed hard goat cheeses, and correlate the sensory scores with the results of all integral parameters investigated under the objective (2); (4) Conduct economic analysis and marketing research on the goat cheese products through extensive consumer acceptability studies in order to determine the sustainability and profitability of dairy goat production.

Impacts and Contributions/Outcomes

We have confirmed that the commercial soft goat cheeses manufactured by licensed goat dairy did not contain detectable levels of pathogenic bacteria including E. coli, coliforms and Staphylococcus aureus, indicating that the soft goat milk cheeses are safe for consumption. Likewise, other soft goat milk cheeses manufactured by other farmstead goat farm can be high quality products if pasteurized and processed properly.

The outcome of this project is anticipated to provide direct beneficial information to especially dairy goat farmers in the Southern Region as well as end-users including consumers, food scientists, members of Georgia Dairy Goat Breeders Association, and other interested clienteles.

Through this research project, we also have provided visitors, consumers, other institution faculty and goat farmers with demonstration and training on goat milk cheese processing technology. Many groups from private sectors, school teachers and children, and especially college faculty and staff members have visited our milk processing facility. We conducted one-day special training workshop on goat milk cheese processing for Drs. Cassandra Vaughn and Evelin Caudra from Alcorn State University, Mississippi on September 10, 2001.

The results of the current investigation are being disseminated to the end-users, such as, and consumers through demonstrations, workshops and newsletters, and also to presentations in scientific conferences and publications in refereed scientific journals.

Publications:

1. Park, Y.W. 2000. Comparison of mineral and cholesterol composition of different commercial goat milk products manufactured in USA. Small Rumin. Res. J. 37: 115-124.
2. Park, Y.W. 2001. Proteolysis and lipolysis of goat milk cheese. J. Dairy Sci. 84. (E. Suppl.): E84-E92.
3. Guo, M.R., P.H. Dixon, Y.W. Park, J.A. Gilmore, and P.S. Kindstedt. 2001. Seasonal changes in the chemical composition of commingled goat milk. J. Dairy Sci. 84.(Suppl.): E79-E83.

Published Abstracts (Conference Proceedings):

4. Park, Y.W., D.L. Van Hekken, M.H. Tunick, and V.H. Holsinger. 2000. Rheological characteristics of young Monterey Jack goat milk cheese. Proc. Int’l. Conf. on Goats, Tours, France. May 14-18, 2000. pp. 601.
5. Van Hekken, D.L. and Y.W. Park. 2000. Electrophoretic characterization of aging Monterey Jack goat cheese. 2000 Joint Meeting of ADSA and ASAS. Baltimore, MD. J. Dairy Sci. Vol. 83. Suppl. 1. p. 83.
6. Van Hekken, D.L., M.H. Tunick, and Y.W. Park. 2000. Rheological properties of aging Monterey Jack goat cheese. 2000 Joint Meeting of ADSA and ASAS. Baltimore, MD. J. Dairy Sci. Vol. 83. Suppl. 1. p. 82.
7. Guo, M.R., P.H. Dixon, Y.W. Park, J.A. Gilmore, and P.S. Kindstedt. 2000. Seasonal changes in the chemical composition of commingled goat milk. 2000 Joint Meeting of ADSA and ASAS. Baltimore, MD. J. Dairy Sci. Vol. 83.Suppl.1. p 8.
8. Park, Y.W. 2000. Proteolysis and lipolysis of goat milk cheese. 2000 Joint Meeting of ADSA and ASAS. Baltimore, MD. J. Dairy Sci. Vol. 83. Suppl. 1. p. 9.
9. Park, Y.W., A. Kalantari, M.R. Lim, K.L.Arora, and J.F. Frank. 2001. Effect of extended refrigerated storage on microbial population of soft goat milk cheeses. The 2001 IFT Proc. Abstract 15C-10, p.23

10. Park, Y.W., A. Kalantari, D.L. Van Hekken, and M.H. Tunick. 2001. Microbiological and rheological characteristics and their association with shelf-life of fresh soft goat milk cheese. J. Dairy Sci. Vol. 84. Suppl. 1:27
11. Van Hekken, D. L., M. H. Tunick, and Y. W. Park. 2001. Protein profiles and rheological properties of fresh goat milk cheese. J. Dairy Sci. Vol. 84. Suppl. 1: 305
12. Kalantari, A., Y. W. Park, and D.L. Van Hekken. 2001. Effects of refrigerated storage
on proteolytic and lipolytic properties of soft goat milk cheeses manufactured in a southern U.S. state. J. Dairy Sci. Vol. 84. Suppl. 1: 305

Collaborators: