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

For the third year of the SARE project, this research was centered on the continued investigation on the feasibility of frozen-storage of goat milk cheeses for extending storage and shelf-life for later marketing. Impacts of 3 month frozen-storage on stability and shelf life of plain soft and Monterey Jack semi-hard goat cheeses were investigated to ascertain the characteristics of changes in chemical, organic acids, rheological, microbial and sensory scores.The three months extended frozen-storage did not have any significant adverse effects on nutritional and sensory properties of the two cheeses, although there were some significant changes in organic acids, rheological indices and microbiological populations with reference to the unfrozen original control goat cheese samples.

Objectives/Performance Targets

1. To investigate the feasibility of extended frozen-storage upto 3 months on food quality of two varieties of goat cheeses (plain soft and Monterey Jack).
2. To study the impact of the extended frozen-storage on changes in the sensory scores and organic acid profiles of the soft and hard goat cheeses.
3. To determine effects of frozen-storage on rheological and microbiological characteristics of the two varieties of goat milk cheeses.

Accomplishments/Milestones

One postdoctoral Research Associates left from our progrm early in the year and replaced in September. For the 3rd year of the project, the effects of extended frozen-storage on chemical, organic acids, rheological, microbiological and sensory characteristics were continuously investigated as the continuation research for the funded project started during the last year in order to explore the feasibility of year-round consistent marketing of the goat cheese products to consumers. Several experiments were conducted on the commercial plain soft (PS) goat cheeses and FVSU manufactured Monterey Jack (MJ) goat cheeses with respect to shelf-life and storage stability of frozen-stored and refrigerated products.

Both varieties were prepared in 3 batches, and divided into three equal portions. One portion was stored as unfrozen control (UFC) at 4¡ÆC for 4 weeks (0, 14, 28 days), and the other two subsamples were frozen at -20¡ÆC and stored for 0 and 3 months (FZC and 3FZ), then immediately thawed at 4¡ÆC, followed by aging at 4oC as was done for UFC. The impacts of 3 months frozen-storage on stability and shelf life of the two varieties of goat cheeses were studied on four quality indices: (1) organic acid profiles, (2) sensory properties, (3) microbiological populations, and (4) rheological and SDS-PAGE characteristics of the products. Organic acids were quantified using a HPLC (Hewlett Packard; LC-1100 Series) equipped with auto sampler, quaternary pump, vacuum degasser and diode array detector. The column was reverse phase Hewlett Packard ODS Hypersil 5mm (125 X 4 mm), and solvent was 0.5% ammonium phosphate. Descriptive sensory properties of the cheeses were evaluated with a trained panel. Flavors and tastes were scored on a 10-point Spectrum intensity scale. Changes in microbial populations were enumerated for total aerobic, E. coli and coliform, yeast and mold, and Staphylococcus aureus using 3M petrifilm techniques. Rheological properties were measured using a universal testing machine and a dynamic analyzer.

The PS cheese contained all tested standard organic acids except pyruvic acid in various amounts including formic, malic, lactic, acetic, orotic, citric, uric, tartaric, and propionic acids. Many unidentified isomeric peaks appeared between the known standard peaks. Lactate was highest organic acid, followed by acetate in PS cheese. Storage treatments (UFC, FZC and 3FZ) significantly (P<0.05) affected most of the identified organic acid contents such as acetate, butyrate, citrate, formate, lactate, malate, orotate isomers, propionate, propionate isomers, a tartarate isomer and uric acid, while aging periods did not influence them. After 2 weeks storage at 4oC, cooked/milky, diacetyl, and milkfat flavors decreased, while yeasty and oxidized flavors increased in PS cheeses (P<0.05). Fresh PS had a sensory quality shelf life of less than 1 month at 4oC. MJ cheeses maintained sensory quality throughout 4 weeks storage at 4oC. Diacetyl flavors decreased and brothy flavors increased (P<0.05) while overall freshness scores did not change. Freezing had no effect on the sensory quality of either type of cheese throughout the subsequent 4 weeks refrigerated storage. Frozen-storage did not affect sensory quality of the two cheeses, which is important for feasibility of frozen-storage of goat cheeses. The pooled data of the respective TPC (log cfu/g) for UFC, FZC, and 3FZ groups of PS and MJ cheeses were: 6.93, 6.67 and 5.51; 8.44, 8.34 and 8.09, indicating that there were significant (P<0.05) reduction in TPC with storage treatments in PS, whereas no difference in MJ cheeses. The TPCs of 0, 14 and 28 days aging at 4oC for corresponding cheeses were: 8.01, 5.67 and 5.52; 8.57, 8.17 and 8.15, revealing that there were significant (P<0.05) decrease in TPC with aging times in both cheeses. UFC cheese had a fragile texture with values of 10.6 N for hardness, 10.1 mm for springiness, 0.10 for cohesiveness, 9.3 for chewiness, 15.9 kPa for elastic modulus, 5.28 kPa for viscous modulus, and 1.75 kPa.s for complex viscosity. Compared to UFC, FZC samples had lower viscoelastic properties and the values decreased further as the cheeses aged. The creation and removal of ice crystals in the cheeses have more effect on the texture of the cheese than on the enzyme activity and extent of protein degradation within the cheese.

Impacts and Contributions/Outcomes

Impact and Contributions/Outcomes:

There were no significant differences in microbial profiles between fresh and frozen-stored cheeses, and reduction of microorganisms in the subsequent frozen-storage indicate frozen-storage of the products appears to be feasible for off-season marketing. There were significant (P<0.05) decrease in total bacterial, yeast and mold counts in both frozen-stored cheeses. There were some changes in organic acids profiles in frozen-stored cheeses. However, freezing had no effect on the sensory quality of either type of cheese throughout the subsequent 4 weeks refrigerated storage. Compared to fresh cheeses, frozen samples had lower viscoelastic properties and decreased further as the cheeses aged. The creation and removal of ice crystals in the cheeses have more effect on the texture and rheology of the cheese than on the enzyme activity and extent of protein degradation within the cheese. These results suggest that the frozen-storage upto three months is feasible for extended storage life, and may be applicable for future production and marketing of the goat milk cheeses for later marketing.
The findings of this year¡¯s research may become the important scientific basis for feasibility of frozen-storage of goat cheese products for off-season marketing, which will be extremely important for the profitability and sustainability of the dairy goat industry. Thre outcome of this research project would be highly beneficial for 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. The funding and implementation of this research project enabled us provid FVSU students, visitors, consumers, other institution faculty and goat farmers with training on goat milk cheese processing technology and development of the products. Many groups from private sectors, school teachers and children, and especially college faculty and staff members have visited our milk processing facility. We continuously disseminate our current findings to the end-users, such as, and consumers through trainings, workshops and newsletters. This project also has especially benefitted to the scientific activities of presentations in national and international scientific meetings and publications in refereed scientific journals.

Publications:

1. Guo, M.R., Y.W. Park, P.H. Dixon, J.A. Gilmore, and P.S. Kindstedt. 2003.
Relationship between the yield of chevre and chemical composition of goat¡¯s
milk. Small Rumin. Research J. In Press.
2. Park, Y.W., A. Kalantari, and J.F. Frank. 2003. Changes in the microflora of
commercial soft goat milk cheese during refrigerated and frozen storage.
Small Ruminant Res. In press.

Published Abstracts (Conference Proceedings):

1. Park, Y.W. and Jung Hoon Lee. 2003. Impacts of Freezing and Thawing on Organic
Acid Contents of Plain Soft and Monterey Jack Caprine Milk Cheeses. 9th World Conf. Animal Production, Porte Alegre, Brazil. Conf. Proc. pp. 271.

2. Lee, S.J., J.H. Lee, J. Rhodes, and Y.W. Park. 2003. Effects of 3 months frozen-
storage and refrigeration on proteolysis of soft goat milk cheeses determined by
SDS-PAGE and gel image analysis. The 2003 ADSA-ASAS Joint Meeting Abst.
No. 281.
3. Lee, S.J., J.J. Lee, A. Kalantari, V. Gutta, and Y.W. Park. 2003. Effects of freezing
and thawing on chemical changes in plain soft and Monterey Jack goat milk cheeses. The 2003 IFT Proc. pp. 19. Abstract No. 14A-14.

4. Lee, J.H., S.J. Lee, A. Kalantari, and Y.W. Park. 2003. Comparison of microbial
populations of unfrozen and frozen control goat cheeses with those of 3 months
frozen-stored ones. The 2003 ADSA-ASAS Joint Meeting Abst. W279.
5. Van Hekken, D.L., M.H. Tunick, D.W. Olson, and Y.W. Park. 2003. Proteolysis and
rheology of soft goat milk cheese after frozen storage. The 2003 ADSA-ASAS Joint Meeting Abst. No. W289.
6. Park, Y.W., S.J. Lee, J.H. Lee, and M.A. Drake. 2003. Effects of freezing and
thawing on sensory properties of plain soft and Monterey Jack goat milk cheeses. The 2003 IFT Proc. pp. 269. Abstract No. 104D-14.

Collaborators: