J. Dairy Sci. 2007. 90:2181-2188. doi:10.3168/jds.2006-506
© 2007 American Dairy Science Association ®
Alternatives for Improving Physical, Chemical, and Sensory Characteristics of Goat Cheeses: The Use of Arid-Land Forages in the Diet
S. Álvarez*,1,
M. Fresno*,
P. Méndez*,
N. Castro
,
J. R. Fernández
and
M. R. Sanz Sampelayo
* Animal Production Unit, Canary Agronomic Science Institute (ICIA), 38200 La Laguna, Tenerife, Spain
Department of Animal Science, Las Palmas de Gran Canaria University, 35416 Arucas, Gran Canaria, Spain
Animal Nutrition Unit, Zaidín Experimental Station, Consejo Superior de Investigaciónes Científicas, 18008 Granada, Spain
1 Corresponding author: salvarez{at}icia.es
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ABSTRACT
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To establish the effect of an alternative diet on the quality of Majorero cheese, the basic physicochemical parameters, fatty acid profile, and sensory characteristics were studied. Two groups of 20 Majorero goats were fed 2 different diets: a forage diet (DF), which had a high ratio of long fiber to concentrates (65:35), and a concentrate diet (DC), with a low ratio of long fiber to concentrates (35:65). The DF dietary fiber was supplied by native forages adapted to arid land. A total of 42 Majorero goat cheeses were used for this study: 21 in the DF group and 21 in the DC group. Seven cheeses from each group were tested after 2, 15, and 60 d of ripening. The milk produced by goats fed the DF diet had a higher fat concentration. No significant differences were observed in the milk fatty acid profile. The diet affected the chemical composition of the cheese in pH and fat content, and fat was significantly higher in cheeses made from DF milk than those from DC milk. Dietary characteristics had important effects on the medium-chain fatty acid composition (C6 to C14) of the cheese fat, giving DF cheeses the specific goat’s milk flavor that is sought after for this type of cheese. The fatty acid composition (%) differed substantially among different ripening times. The DF cheeses were more appreciated by the panelists, as they had a greater variety of odors and flavors than the DC cheeses. The DF hard cheeses were described as having vegetable and fruity tones as well as tones of hay and dried fruit.
Key Words: goat’s milk and cheese • fiber-to-concentrate ratio • chemical composition • sensory property
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INTRODUCTION
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It is empirically accepted that the type of pasture influences the chemical composition and sensory properties of cheese (Verdier-Metz et al., 1998; Bugaud et al., 2001). However, a reduction in the proportion of forage in the diet can induce a decrease in the milk fat content (Morand-Fehr and Sauvant, 1980; Economides et al., 1989).
Two main dietary factors can clearly modify the fatty acid (FA) composition of goat’s milk and cheeses: 1) the supply and nature of fiber sources and 2) the supply and characteristics of lipids in the diet (Morand-Fehr et al., 2000). Lipid composition is one of the most important components of the technological and nutritional quality of goat’s milk, and lipids are involved in cheese yield (per kilogram of milk), firmness, and the color and flavor of goat dairy products (Delacroix-Buchet and Lamberet, 2000). In addition to their quantitative contribution to the amount of dietary energy, the different FA are also potentially involved as positive or negative predisposing factors in the health of human consumers (Parodi, 1999; Williams, 2000). Futhermore, the peculiarities of the goat’s milk lipolytic system (Chilliard, 1982) and content of medium-chain FA (Ha and Lindsay, 1993) could greatly change the FFA content, playing a major role in the distinctive goat’s milk flavor (Chilliard et al., 2003).
Studies related to the influence of ruminants’ feeding regimen on the sensory properties of cheese are particularly important when the product has been designated as Protected Designation of Origin (PDO), because the feeding regimen constitutes one of the bases of the PDO relationship with the land where cheeses are produced (Grappin and Coulon, 1996).
This study is part of a project aimed at demonstrating the effects on the characteristics of milk used in Canarian PDO cheese when goats are fed diets with varying ratios of different kinds of forage. Because the goat industry has become more intensive, with higher milk yields, goats have been receiving a diet with 50% less fiber. These diets, which are too rich in energy because of a high percentage of concentrates (more than 50% of DM), significantly decrease the milk fat content, reducing the life expectancy of the animals and causing many health problems (Gutiérrez et al., 1999). The Canary Islands, like many other arid areas, have scarce pasture resources, and this problem cannot be solved simply by importing forage because of the high cost of its transport; therefore, the production of native forages or those that are properly adapted to theses habitats can help to reduce this problematic situation. Furthermore, this encourages the development of livestock farming, which aids in conservation of the environment by recovering areas of forage production that are now severely deteriorated.
The aim of the present paper was to determine the effect of 2 diets on the physicochemical and sensory characteristics of Majorero cheese: one with a high ratio of long fiber to concentrate (65:35), based on forages adapted to arid conditions (forage diet, DF), and the other with a low ratio of long fiber to concentrate (35:65; concentrate diet, DC), the latter being the diet most often used by Canarian farmers in these arid zones. The study was undertaken in experimental conditions to determine the effects of diet and ripening on the quality of the cheeses. Goat breed, husbandry, and cheese-making practices were based on the instructions given for PDO Majorero cheese (Boletin Oficial del Estado).
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MATERIALS AND METHODS
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Experimental Design and Procedure
Forty multiparous Majorero goats were divided into 2 equal groups based on their lactation number, milk production, and type of kidding. These animals had kidded in the traditional season (December), and the trial began in March (midlactation period). From 4 wk before the beginning of the experiment, one group (DF) was fed a diet of vinagrera (Rumex lunaria), saltbush (Atriplex halimus), and barley (Hordeum vulgare) hay, whereas the other group (DC) received only cereal straw as a fiber source. The 2 diets were supplemented with a commercial concentrate for goat’s milk production and a mixture of corn, barley grain, and dehydrated alfalfa. The amount of concentrates given was determined for the whole experiment to cover the same maintenance and milk production requirements as INRA recommendations (INRA, 1990). These quantities remained unchanged throughout the experiment, although they differed between one group and the other. The concentrates made up 35% (DF group) and 65% (DC group) of the total DM in the diet. The characteristics of the different feeds are specified in Tables 1
and 2. During the experimental period, the quantities of each diet provided were calculated and controlled to ensure an identical supply of energy and protein.
Cheese Samples
For 4 consecutive days during the experimental period, milk produced by each of the 2 experimental groups was processed to make cheese. Overall, 8 cheese-making processes were completed in a semitraditional factory placed in the Animal Production Unit; every day, 2 vats were filled with 50 kg of milk, one with DF milk and the other with DC milk. Cheeses were made according to the specifications of the Majorero Cheese Denomination of Origin Regulatory Board (Orden Ministerial de 16 de febrero de 1996). The cheeses were made on the same day as milking. Milk was not pasteurized and no starter culture was added. After heating to 30 ± 1°C, the animal rennet commonly used by farmers (commercial rennin powder, Marshall rennet power 50% chymosin and 50% pepsin) was added, following the manufacturer’s instructions, to obtain clotting within 30 to 35 min. After coagulation, all curds were cut to obtain grains the size of millet. The presses were the same for all cheeses: 4.9 kPa for 5 h. Afterward, salting was achieved by rubbing dry salt onto the surface of the cheeses. A total of 42 Majorero goat cheeses were used for this study: 21 DF and 21 DC. Seven cheeses were analyzed from each group after 2, 15, and 60 d of ripening. Half of each cheese was used for the physicochemical analysis and the other half was used for the sensory analysis. Cheese samples were coded with a letter representing the respective diet used for feeding the goats and with a number. During ripening, the cheeses were stored in a ripening chamber at 10 to 12°C and 85 to 86% relative humidity.
For each ripening time, cheeses were sent to the laboratory in refrigerated boxes and a basic chemical analysis was performed immediately. Cheeses samples were vacuum-packed and stored at –20°C for FFA analysis. Immediately before analysis, the samples were defrosted overnight at 20°C. For the sensory analysis, all samples were wrapped in aluminum sheets, stored under refrigerated conditions, and placed at room temperature (20 ± 1°C) for 2 h before testing.
Physicochemical Analysis
Milk.
The protein, fat, lactose, and DM contents were measured in a representative sample taken from the vat of each cheese, using a MilkoScan 133B (Foss Electric, Slangerupgad, Denmark). The pH value was determined at room temperature (20°C) using an inoLab pH Level 1 pH meter (inoLab, Weilheim, Germany). Another sample was frozen at –20°C for FFA analysis.
Cheese.
Each cheese sample was analyzed 3 times by near-infrared spectroscopy (Instalab 600, Foss Electric), with previous calibrations: total solids by standard FIL-IDF 4A (IDF, 1982), fat by standard FIL-IDF 52 (IDF, 1991), and total nitrogen by standard FIL-IDF 220B (IDF, 1993). Cheese pH was measured at 20°C by introducing a penetrometric electrode into the cheese. The pH value was determined at room temperature (20°C) using an inoLab pH Level 1 pH meter.
FFA.
The extraction of total FFA and their qualitative and quantitative determination were performed using a modification of the method of Sukhija and Palmquist (1988). In particular, the FA composition of milk and cheese fat was evaluated by gas chromatography. Fatty acid methyl esters were separated on an Autosystem gas chromatograph (PerkinElmer, Norfolk, CT) fitted with an SP-2560 fused-silica capillary column [100 m x 0.25 mm (i.d.), 0.20 µm of film, Supelco, Bellefonte, PA] equipped with a flame-ionization detector. The temperature was programmed from 150 to 185°C at 5°C/min, held for 30 min, then increased to 230°C at 5°C/min, and held for 26 min. The carrier gas was N2. Injector and detector temperatures were 250 and 300°C, respectively. The peaks for individual FA were identified using pure methyl ester standards (Supelco). Peak areas for individual FA were corrected for recovery using butter oil as a reference standard (CRM 164, Commission of the European Community Bureau of References, Brussels, Belgium).
Sensory Analysis
Sensory analyses were carried out after 2, 15, and 60 d of ripening. Samples, coded with random 3-digit codes (Meilgaard et al., 1991), were presented in a balanced way (Suriyaphan et al., 2001) to avoid the effect of the presentation order. Cheeses were served without any identification of the origin of the milk used (DF vs. DC). The methodology used was described previously; odor and flavor attributes were in accordance with those described by Beródier et al. (1996) and texture followed the guidelines published by Lavanchy et al. (1999). The group of 7 judges were highly experienced and had been formally trained over 10 yr; this panel works in collaboration with the PDO Majorero cheese sensory panel. Before beginning this experiment, 5 extra training sessions were performed with Majorero PDO cheeses.
The cheese samples presented were 1.5 cm thick x 1.5 cm wide x 5 to 8 cm long with the rinds cut away. The size and shape of all pieces were identical. Two portions per sample were served, one to evaluate texture and the other to evaluate odor and flavor (Lavanchy et al., 1999). Serving temperature was 20 ± 1°C (Engel et al., 2000). Judges rinsed their mouths between the 2 samples using unsalted crackers, Granny Smith apples, and water with a very low level of mineralization to remove any aftertaste. The sensory analysis was conducted in a special room of the ICIA following the instructions given by the UNE 87-004 norm (IRA-NOR, 1979).
Seventeen sensory attributes, 7 for texture (roughness, moisture, elasticity, firmness, friability, adhesiveness, and solubility) and 10 for odor and flavor (saltiness, sweetness, bitterness, acidity, pungent, astringent, residual taste, taste persistence, odor, and flavor intensity) were scored on a structured scale from 0 to 7. Roughness and moisture were scored from 0 to 4 and from 0 to 5, respectively. In addition, each assessor was allowed to describe the odor and flavor of each sample by selecting descriptors from the following main family list: milky, vegetable, fruity, toasted, animal, floral, spiced, and others (soap, rancid, and pungent in the nose). Despite all these descriptive characteristics, the panelists also evaluated (on a scale from 0 to 7) their preferences on the cut aspect, texture, odor, flavor, and taste of the cheeses.
Statistical Analysis
The software package SPSS version 11.0 (SPSS Inc., Chicago, IL) was used for statistical processing of the results. A GLM was used to establish statistical differences between the physicochemical parameter values and sensory analysis scores according to the type of diet, ripening time, and the interaction between these 2 factors. Posthoc multiple analyses by Tukey’s test were used for the ripening time factor.
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RESULTS AND DISCUSSION
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Physicochemical Characteristics
Milk.
Table 3 contains the mean values for analytical characteristics of the goat’s milk used. As expected, all the parameters considered fell within the range of values expected for this type of milk. As may be noted, a greater amount of fat (P < 0.01) was found in the DF milk (43.9 g/kg) than in the DC milk (39.2 g/kg). This seemed to indicate an adequate proportion of large fiber in the DF diet and an excessive percentage of concentrates in the DC diet (Letorneau et al., 2000). This fact could be explained by the decrease in the forage-to-concentrate ratio of the diet and the decrease in particle size of the fiber. The fat content of the milk produced tended to be lower in the DC milk, perhaps because of a reduction in the acetic acid produced, which is a principal precursor of the FA synthesized in the mammary gland (Dils, 1986; Vermorel, 1990).
These results, which showed an increase in fat (P < 0.01) and protein (nonsignificant) in DF milk, can be used by PDO technicians as an economical argument to urge farmers to change their animal feeding management. Because all Majorero milk is transformed into cheese, better DF cheese yield results (data not shown) could support this proposal.
Other authors (Verdier-Metz et al., 2000; Bugaud et al., 2001) have demonstrated a milk fat increment when comparing different pastures and hays; however, no significant differences were found in similar studies (Buchin et al., 1999; Pirisi et al., 2001). Sanz Sampelayo et al. (1998), comparing forages of different physical forms, found that goats appeared to be more sensitive to energy intake than to the characteristics of the diet. The other contents of the milk analyzed were very similar for both types of diet, except lactose, which was higher in the DC group (P < 0.05). The pH value did not differ substantially in either diet. These pH values could result in similar coagulation properties for cheese making (Pirisi et al., 2001).
Table 4 shows the FA composition of the milk fat from goats fed each diet. The most abundant FA in both types of milk were capric, myristic, palmitic, and oleic acids. Other authors have reported similar findings in different goat’s milks (Fontecha et al., 1990; Sanz Sampelayo et al., 1998). Medium-chain FA containing between 6 and 14 carbons represented 34.9 and 35.3% of the total FA for the milk fat from goats consuming diets DF and DC, respectively.
No effect on the FA composition of the milk fat was observed when comparing different dietary characteristics. When the milk fat content of ruminants decreases because of alterations in the diet, the FA composition of the milk also changes. The proportion of unsaturated FA increases and the proportion of saturated FA decreases (Rook, 1976). Such changes were not observed in the present study, in accordance with the findings of Sanz Sampelayo et al. (1998). As described by Bas et al. (1998), the synthesis of microbial lipids in the rumen is very active in goats. The proportion and type of roughage in the diet modify the composition of microbial lipids, more specifically the ratio of 18:0 to 18:1 and the percentage of minor FA. This ratio was different for the experimental milks (lower in DC milk: 0.28 vs. 0.34), but there were no changes in the percentage of short-chain FA.
Cheese.
Table 5 presents the mean values for pH, moisture, fat, protein, and fat in DM over ripening (at 2, 15, and 60 d) for the types of cheese considered. The chemical composition was affected by the diet in pH and fat content. Fat was significantly higher in cheeses made from DF milk than those from DC milk (P < 0.001). This could be due to the high fat content of the DF milk, which significantly influenced cheese composition. However, similar results were not always observed when ruminants were fed different diets (concentrate vs. pasture; Pirisi et al., 2001).
Ripening time affected nearly all physicochemical parameters. Fat and protein contents rose significantly over the ripening period, whereas moisture decreased. The moisture values were similar to those reported by Martín-Hernández et al. (1992) but were considerably lower than those determined by Fontecha et al. (1990) for artisanal Majorero cheese, in which ripening takes place at ambient temperature and low relative humidity. Significant differences were observed in pH because of the diet and ripening. Cheese pH decreased up to 15 d and increased considerably between 15 and 60 d, attaining values similar to those of fresh cheeses, thus confirming the important metabolic activity of lactic acid bacteria in this period.
Table 6 shows the mean profile for the main FA in the experimental cheeses. Dietary characteristics had important effects on the medium-chain FA composition (C6 to C14) of the cheese fat. Within long-chain FA, only the stearic acid concentration differed between the 2 groups. Saturated FA constituted 76.08 and 76.25% of the cheese fat from goats fed the DF and DC diets, respectively.
According to the type of diet, the FA profile of the cheeses showed differences (P < 0.05); in spite of that and in accordance with their respective values, these results cannot be considered relevant. In this respect, the most important aspect was the different concentrations of milk fat according to the type of diet; DF milk presented 43.9 g/kg of fat, whereas the value for DC milk was 39.2 g/kg. In addition to medium-chain FA (C6 to C14), conjugated linoleic acid and polyunsaturated FA are important because of their aromatic and health aspects (McGuire and McGuire, 2000; Haenlein, 2004); and the changes in these acids as an effect of the DF and DC diets were 16.2, 0.22, and 1.61 g and 14.52, 0.22, and 1.39 g, respectively.
The more elevated amount of fat in the DF milk implied higher concentrations of nearly all FFA in the DF cheeses. Furthermore, medium-chain FA play a major role in the characteristic goat flavor of these types of cheese (Chilliard et al., 2003), and the content of the FA was higher, but not significant, in the DF milk.
The fatty acid composition differed substantially among the different ripening times. The C4 to C12 FA had similar concentrations at 2 and 15 d of ripening, and increased their values until 60 d of maturity. On the other hand, the concentrations of stearic, oleic, linoleic, and conjugated linoleic acids decreased after d 15 of ripening. These FA are potentially involved as positive or negative predisposing factors in the health of human consumers (Williams, 2000). The C4 to C10 FA concentration provides a specific goat’s milk flavor that is sought after in this type of cheese. Of the FFA, octanoic acid is known to be the one from the lipid fraction principally responsible for the goat’s milk flavor, because it is perceived even at low proportions and is present at levels higher than the perceptual threshold (Le Queré et al., 1998). This acid was significantly higher (P < 0.001) in the DF cheeses and also in cheeses ripened for 60 d (P < 0.001).
As described by some authors (Dils, 1986; Vermorel, 1990), it is possible to understand that diets richer in fiber produce more VFA in the rumen, and for this reason, the synthesis of FA with less than 18 carbons increases. The proportion of short-chain FA in the 3 ripening stages was considerably lower, not only than that recorded for artisanal Majorero cheese using unpurified rennet pastes obtained by macerating kids’ stomachs (Fontecha et al., 1990), but also compared with data from industrial Majorero cheeses using commercial rennet (Martín-Hernández et al., 1992).
Sensory Analysis.
Results of the sensory evaluation of the DF and DC cheeses are shown in Table 7 for texture, odor and flavor descriptors, and preference attributes. Diet affected 4 of the 7 texture attributes. The DF cheeses were less firm and friable (P < 0.001), characterized by a higher moisture and solubility value. On the other hand, roughness, elasticity, and adhesiveness were very similar for both types of cheeses. Verdier Metz et al. (2000, 2002), comparing diets with different botanical species, found different values for firmness and solubility in the experimental cheeses.
The odor and aroma intensity were significantly higher for DF cheeses, with lactic and grass descriptors that could be correlated with the higher composition of medium-chain FA in the DF cheeses. These differences could be due to the presence in the milk of some chemical elements that came directly from the forage, which played a direct role in the odor and aroma or an indirect role in the ripening process (Martin and Coulon, 1995).
The DF cheeses were sweeter, with lower values for bitterness, acidity, pungency, and astringency characteristics. The DF cheeses were more appreciated by the expert panel, presenting higher values for texture, odor, flavor, and taste attributes.
The evaluation of expert judges was in agreement with a consumer panel (100 to 150 people, data not shown). Texture hedonic results could be related to the higher fat content in DF cheeses, with more solubility but less firmness and friability. Preference in taste could be related to less acidity and bitterness and also to lower trigeminal sensation values. Both judges and consumers preferred the DF cheeses in their odor and flavor evaluations because of the higher intensity and more complex descriptors (vegetable, fruity, and hay descriptors).
Ripening time affected all the sensory parameters analyzed. The odor and aroma intensity increased during ripening for both the DF and DC cheeses. This increase is associated with a progressive reduction of lactic family descriptors (Muir et al., 1997). As the cheeses matured and became drier, they became firmer and more crumbly. Trigeminal stimulation increased with the ripening process. Lemieux and Simard (1994) referred to a frequent correlation between bitterness and astringency; this started to appear slightly in the cheeses after 15 d and became stronger tasting at 60 d. The DF cheeses had a greater variety of odors and flavors than did the DC cheeses. The DF cheeses at 60 d of ripening presented vegetable and fruity characteristics as well as those of hay and dried fruit.
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CONCLUSIONS
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The use of a diet (DF) with a long fiber-to-concentrate ratio (65:35) based on forage adapted to arid conditions compared with another diet (DC) with a low fiber-to-concentrate ratio affected the quality of the cheese. Fat composition was higher in the DF cheeses, and this fact had an important effect on the medium-chain FA composition (C6 to C14). These chemical results could be related to particular sensory properties such as odor and flavor descriptors. Expert judges found differences in texture, odor, flavor, and taste. The DF cheeses were more appreciated by the expert panel and also by a consumer test. This fact could be due to less acidity and trigeminal sensation and more solubility, taste persistence, and odor and flavor intensity as well as the presence of vegetable, fruity, and dried fruit descriptors. This study demonstrates the importance of including long fiber from local forages in the diet of goat breeds in arid zones, especially when milk is transformed into PDO cheeses.
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ACKNOWLEDGEMENTS
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This study was supported financially by the Instituto Nacional de Investigación y Tecnologia Agraria y Alimentaria, Programo Nacional de Recursos y Tecnologias Agroalimentarias. 01-Project and was continued in the Denominación de Origen Quesos de Canarias of the Canary Government project. In addition, the authors would like to thank Heather R. Briggs for reviewing the English grammar for the paper.
Received for publication August 3, 2006.
Accepted for publication December 19, 2006.
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ABSTRACT
INTRODUCTION
