Effect of optimized humectant treatments on the quality characteristics of goat milk soft cheese: A comparative study

Introduction

Goat milk soft cheese has drawn growing interest for its digestibility, distinct flavor, and nutritional edge over cheese made from cow's milk. Smaller fat globules, a higher share of medium-chain fatty acids, and a comparatively weak protein matrix all make goat milk easier to digest and well suited to soft cheese production (Park et al., 2007; Clark and Mora García, 2017) [4,18] . Beyond its processing advantages, goat milk itself carries recognized dietary value, including easier tolerance among individuals sensitive to cow milk proteins (Goswami et al., 2017) [12] . The trade-off is moisture: soft cheese holds a lot of water, which leaves it prone to textural breakdown, syneresis, spoilage, and a short shelf life. Controlling moisture and water activity is therefore central to keeping the product safe, stable, and acceptable to consumers (Fennema, 2008) [7] . Much of that moisture instability traces back to syneresis, the contraction of the casein network after coagulation that squeezes whey out of the curd. Dejmek and Walstra (2004) [5] reported that the rate and extent of syneresis in rennet-induced curd are primarily governed by the microstructure and surface characteristics of casein micelles. Following gel formation, moisture retention is largely determined by the rearrangement and contraction of the protein matrix rather than by subsequent processing interventions. Consequently, humectants provide an effective approach for modulating moisture retention in soft cheese, as they influence the water phase after curd formation without altering the coagulation mechanism or the overall cheese-making process. According to Rahman (2007) [19] , foods with a water activity ranging from approximately 0.60 to 0.85 are classified as intermediate-moisture foods. The microbial stability of these products is achieved through the incorporation of humectants or other water-binding solutes, which lower water activity without requiring extensive dehydration or continuous refrigeration. Humectants are food-grade compounds that bind water and lower water activity without removing much moisture from the food itself. Researchers have looked at them as a way to improve texture, control moisture movement, and extend shelf stability (Khanam et al., 2017) [16] . Glycerol and sorbitol, both polyhydric alcohols, are common choices because their hydrophilic groups form hydrogen bonds with water and limit how much of it stays free (Grembecka, 2015) [13] . Earlier work has shown that adding humectants changes the physicochemical makeup, texture, and sensory profile of intermediate-moisture foods (Gliemmo et al., 2006; Chen et al., 2014) [3,10]: they bind free water and, in doing so, shift moisture distribution, texture, and microbial stability, which together affect overall quality. Their use in goat milk soft cheese specifically has not been studied much and still needs systematic optimization. Humectants have been studied fairly widely for food preservation, but goat milk soft cheese remains a gap. Few studies have looked closely at optimized glycerol and sorbitol levels in this product, particularly how the two compare on physicochemical properties, texture, colour, and sensory acceptance under the same formulation conditions (Livesey, 2003) [17] . The present study was aimed to evaluate and compare the quality characteristics of goat milk soft cheese prepared using the pre-optimized humectant treatments, selected through preliminary optimization trials based on sensory acceptability. Additionally, the study sought to determine the relative effectiveness of humectants in improving moisture regulation and product stability, thereby contributing to the development of high-quality intermediate-moisture goat milk soft cheese.

Materials and Methods Experimental Design

The work was carried out at the Department of Livestock Products Technology, DUVASU, Mathura, India. Treatments identified as optimal in preliminary trials were carried forward for detailed evaluation, with the goal of understanding how optimized glycerol and sorbitol incorporation affects the quality of goat milk soft cheese. Goat milk soft cheese was prepared from standardized goat milk under controlled laboratory conditions. Two preliminary sub-experiments were undertaken to improve the quality of developed product incorporating two humectants i.e. glycerol and sorbitol separately at 2%, 4%, and 6%, in which 4% glycerol (G2) and 4% sorbitol (S2) were selected on the basis of sensory evaluation. The selected treatments were further compared with control (C) to select the best treatment to have well accepted goat milk soft cheese with desirable characteristics. The method of goat milk soft cheese preparation has been given in flow diagram 1.

Flow diagram 1: Preparation of goat milk soft cheese

Product analysis

Cheese samples were tested for pH, titratable acidity, total solids, moisture, protein, fat, fat on a dry matter basis, and ash content, following the standard procedures of AOAC International (2016) [1] . Water activity was measured in triplicate with a calibrated water activity meter (AquaLab 3TE, Decagon Devices Inc., Pullman, WA, USA). Yield and °Brix values were measured with a digital refractometer (Atago RX-5000i, Japan) following standard analytical procedures. All determinations were run in triplicate, and results are reported as mean ± standard error. Texture profile analysis (TPA) measured adhesiveness, springiness, cohesiveness, gumminess, chewiness, and resilience using a texture analyzer (TA.HD Plus, Stable Micro Systems, UK) under standardized test conditions. Samples went through double compression cycles, and textural parameters were calculated from the resulting force-time curves. Lightness (L*), redness (a*), and yellowness (b*) were measured with a Hunter colorimeter (Colour Tech PCM+, Colour Tec Associates Inc., Clinton, NJ, USA). The instrument was calibrated against standard white and black tiles before each session. A semi-trained panel of seven postgraduate students and faculty from the Veterinary College, DUVASU, Mathura, evaluated the samples. Panelists scored colour and appearance, flavor/odor, body and texture, acidity, saltiness, and overall acceptability on a 9-point hedonic scale (1 = extremely disliked; 9 = extremely liked), following Keeton (1983) [15] . Evaluation sessions ran in the late afternoon, around 4:00 p.m., under controlled conditions. Panelists worked without interacting with one another, and lukewarm water was provided between samples to cleanse the palate.

Statistical Analysis

Data were analyzed in SPSS (version 20.0) using a completely randomized design, with triplicate experiments and duplicate observations for each parameter (n = 6 per treatment; 21 observations overall). One-way analysis of variance (ANOVA) was applied, and means were separated using Duncan's Multiple Range Test (DMRT) at P<0.05, following the procedures described by Snedecor and Cochran (1995) [20] .

Results and Discussion

Physico-chemical Properties: The physico-chemical characteristics of goat milk soft cheese prepared with incorporation of humectants are presented in table 1. The pH, moisture content, fat on dry matter basis content and water activity values of C were significantly (P<0.05) higher whereas titratable acidity and brix values of C were significantly (P<0.05) lower than G2 and S2, however there was no significant difference between G2 and S2 for both the parameters. The lower moisture content observed in G2 and S2 likely reflected additional syneresis induced by the humectants themselves, in addition to the whey loss that occurred during the initial curd formation. As described by Dejmek and Walstra (2004) [5] for rennet curd systems, once the casein network was established, any factor that altered the distribution of water between the protein matrix and the surrounding serum, including the addition of solutes with a strong affinity for water, could promote further contraction of the protein network. As per Chen et al. (2014) [3] , water exists in three general forms in food matrix (1) free, unbound water;

(2) free, immobilized water; (3) chemically bound water. Humectants attract water to themselves in meat products by chemical bonds, so they potentially reduce the moisture content of products due to underestimation of water content. They are believed to reduce aw of a product due to the presence of hydrophilic group such as hydroxyl groups, which have affinity to form hydrogen bonds with molecules of water, thus decreasing the availability of free water (Gliemmo et al., 2006) [11] . The reduction in water activity observed in G2 and S2 was attributed to the strong waterbinding capacity of glycerol and sorbitol, which converted free water into a bound form, thereby limiting water availability to microorganisms and contributing to product stabilization. Total solid content of S2 was significantly (P<0.05) higher than C and G2 indicating that sorbitol did a better job of regulating moisture than glycerol. Badola et al. (2017) [2] , while evaluating several humectants in a model khoa system, reported that sorbitol produced the greatest reduction in water activity among the compounds tested, supporting the notion that the water-binding capacity of sorbitol was not specific to a single dairy matrix but was applicable across different milk-based products. There was no significant difference in yield%, protein, fat and ash content between control and treatments.

Texture Profile Analysis

The texture profile analysis values of goat milk soft cheese prepared with incorporation of humectants are presented in table 2. The adhesiveness, gumminess and chewiness values of G2 and S2 were significantly higher (P<0.05) than C; however there was no significant between G2 and S2 for these parameters. Higher textural values of treatments might be due to water binding capacity of humectants resulting into low moisture content and more viscous product. The lower moisture content and increased binding of free water likely contributed to this effect; with reduced availability of free water, protein-protein interactions were strengthened, resulting in a denser protein network. 2006) [10,22] reported similar relationships between moisture content and firmness in other dairy matrices. The increased gumminess and chewiness exhibited by the treated samples were attributable to their higher total solids content, as these textural parameters are indicative of the resistance of the cheese matrix to deformation and the energy required during mastication. The reduction in moisture content facilitated closer packing of casein micelles, leading to enhanced rigidity and structural integrity of the protein network. This inverse relationship between moisture content and textural firmness has been extensively reported in intermediate-moisture foods (Fennema, 2008) [7] . There was no significant difference in springiness, cohesiveness and resilience values between control and treatments suggesting the cheese's viscoelastic balance held steady regardless of humectant. In other words, the humectants affected firmness without touching the network's elastic recovery, a finding in line with Gunasekaran and Ak (2003) [14] , who found that moderate compositional shifts do not necessarily change the elastic behavior of soft cheese. The relationship between reduced moisture content and increased firmness has been well documented in cheese science literature. Foegeding and Drake (2007) [9] , in their review of the sensory and mechanical properties of cheese texture, reported that increased structural compactness and chewiness were with the progressive tightening of the protein network around a diminished pool of free water. A similar mechanism likely accounted for the increased firmness, gumminess, and chewiness observed in G2 and S2 compared with the control (C), where reduced moisture content promoted the formation of a more compact and rigid protein matrix.

Instrumental color anaylsis

The instrumental color values of goat milk soft cheese prepared with incorporation of humectants are presented in table 3. There was no significant difference in lightness and yellowness values between control and treatments, however redness values of G2 and S2 were significantly (P<0.05) higher than C. Generally, humectants attract water resulting in low moisture levels and helps to prevent intermediate moisture in products from drying out, leading to increasing light-scattering and producing lighten finish product, however it depends on nature of humectants (Fernandez-Lopez et al., 2003). It might be the possible reason for the higher redness values of G2 and S2 than C. Sorapukdee et al. (2016) [21] also observed significantly (P<0.05) higher redness (a*) values of spent hen meat jerky incorporated with glycerol at 10 and 15% level than control.

Sensory Evaluation

The sensory scores of goat milk soft cheese prepared with incorporation of humectants are presented in table 4. There was no significant difference in color and appearance scores between control and treatments, as also supported by instrumental colour values and suggesting the cheese's visual appeal held steady regardless of treatment. Flavor as well as body and texture scores of S2 were significantly (P<0.05) higher than C and G2, where no significant difference was observed between C and G2. The mild sweetness and balanced acidity that sorbitol brought likely explained the stronger flavor and aroma scores, and the improved body and texture ratings lined up with S2's higher total solids and more even moisture distribution. Lower sensory scores of G2 might be due to thick gel formation and stickiness of product as compared to S2, again addition of glycerol masked the mild acidic flavor of goat milk soft cheese. The comparatively lower sensory acceptance of G2 might also be due to the highly hygroscopic nature of glycerol, which could have imparted a slightly viscous or syrupy mouthfeel. Similar effects of polyols on mouthfeel characteristics have been reported in other dairy and intermediate-moisture food systems (Fennema, 2008; Gunasekaran and Ak, 2003) [7,14] . Acidity, saltiness and overall acceptability scores of C and S2 were significantly (P<0.05) higher than G2, however there was no significant difference between C and S2. Higher sensory scores of S2 might be due to slight sweetish-acidic flavor and aroma provided by sorbitol which was much liked by sensory panelists. The pattern of stronger discrimination for flavor and overall acceptability than for appearance also matches general observations on dairy sensory testing. Drake (2007) [6] , reviewing sensory analysis methods for dairy foods, noted that flavor and texture attributes usually drive consumer acceptability more than visual appearance, since appearance differences tend to be too subtle for a panel to reliably distinguish unless a formulation change is fairly severe. Therefore, S2-goat milk soft cheese with 4% sorbitol as humectant was selected as the best treatment and used as control in next experiment.

Conclusion

Incorporation of humectants improved the overall quality characteristics of goat milk soft cheese, with sorbitol proving to be more effective than glycerol. The addition of 4% sorbitol produced cheese with desirable physico-chemical and textural attributes, characterized by lower water activity, higher total solids, and improved body and texture, while maintaining acceptable colour characteristics. Furthermore, the sorbitol-treated cheese received the highest sensory scores for flavour, mouthfeel, and overall acceptability, indicating its suitability for consumer preferences. The use of sorbitol as a humectant offers a practical approach for developing value-added goat milk products with enhanced quality and marketability. Commercial adoption of this technology could contribute to better utilization of goat milk, diversification of dairy products, and increased income opportunities for goat farmers and small-scale dairy processors, thereby supporting rural livelihoods and promoting the sustainable growth of the goat dairy sector.

References

1. AOAC International. Official methods of analysis of AOAC International. 20th ed. Rockville (MD): AOAC International; 2016.
2. Badola R, Panjagari NR, Singh RRB, Singh AK, Shaik AH. Effect of selected humectants as water activity modifiers on the quality of model khoa system. Indian J Dairy Sci. 2017;70(2):177-183.
3. Chen X, Zhou GH, Xu XL, Liu Y. Effects of humectants on physicochemical and sensory properties of meat products. Food Chem. 2014;147:1-7.
4. Clark S, Mora García MB. A 100-year review: Advances in goat milk research. J Dairy Sci. 2017;100(12):1002610044.
5. Dejmek P, Walstra P. The syneresis of rennet-coagulated curd. In: Fox PF, McSweeney PLH, Cogan TM, Guinee TP, editors. Cheese: Chemistry, Physics and Microbiology. Vol. 1. 3rd ed. London: Elsevier Academic Press; 2004. p. 71-103.
6. Drake MA. Invited review: Sensory analysis of dairy foods. J Dairy Sci. 2007;90(11):4925-4937.
7. Fennema OR, editor. Fennema's Food Chemistry. 4th ed. Boca Raton (FL): CRC Press; 2008.
8. Fernández-López J, Fernández-Ginés JM, AlesonCarbonell L, Sendra E, Sayas-Barberá E, Pérez-Alvarez JA. Application of functional ingredients in meat products. Meat Sci. 2004;68(1):1-17.
9. Foegeding EA, Drake MA. Invited review: Sensory and mechanical properties of cheese texture. J Dairy Sci. 2007;90(4):1611-1624.
10. Fox PF, Uniacke-Lowe T, McSweeney PLH, O'Mahony JA. Fundamentals of Cheese Science. 2nd ed. Cham: Springer; 2017.
11. Gliemmo MF, Campos CA, Gerschenson LN. Effect of several humectants and potassium sorbate on the growth of Zygosaccharomyces bailii in model aqueous systems resembling low-sugar products. J Food Eng. 2006;77(4):761-770.
12. Goswami M, Bharti SK, Tewari A, Sharma H, Karunakara KN, Khanam T. Implication of functional ingredients of goat milk to develop functional foods. J Anim Feed Sci Technol. 2017;5(2):65-72.
13. Grembecka M. Sugar alcohols their role in the modern world of sweeteners: A review. Eur Food Res Technol. 2015;241(1):1-14.
14. Gunasekaran S, Ak MM. Cheese Rheology and Texture. Boca Raton (FL): CRC Press; 2003.
15. Keeton JT. Low-fat meat products: Technological problems with processing. Meat Sci. 1993;36(1-2):261276.
16. Khanam T, Goswami M, Pathak V, Bharti SK, Karunakara KN. Effect of sorbitol incorporation on quality characteristics of chicken meat spread. Indian J Poult Sci. 2017;52(3):318-321.
17. Livesey G. Health potential of polyols as sugar replacers, with emphasis on low glycaemic properties. Nutr Res Rev. 2003;16(2):163-191.
18. Park YW, Juárez M, Ramos M, Haenlein GFW. Physicochemical characteristics of goat milk. Small Rumin Res. 2007;68(1-2):88-113.
19. Rahman MS, editor. Handbook of Food Preservation. 2nd ed. Boca Raton (FL): CRC Press; 2007.
20. Snedecor GW, Cochran WG. Statistical Methods. 8th ed. Ames (IA): Iowa State University Press; 1989.
21. Sorapukdee S, Sittipod S, Charoenrein S. Effect of moisture content and composition on colour stability and light scattering properties of meat products. Food Chem. 2016;196:1093-1100.
22. Walstra P, Wouters JTM, Geurts TJ. Dairy Science and Technology. 2nd ed. Boca Raton (FL): CRC Press; 2006.