Gouda Cheese Research Articles

Determination of Microbial Diversity in Gouda Cheese via Pyrosequencing Analysis

The present study aimed to investigate the microbial diversity in Gouda cheese within the four months of ripening, via next-generation sequencing (NGS). Lactococcus (96.03%), and Leuconostoc (3.83%), used as starter cultures, constituted the majority of bacteria upon 454 pyrosequencing based on 16S rDNA sequences. However, no drastic differences were observed among other populations between the center and the surface portions of Gouda cheese during ripening. Although the proportion of subdominant species was <1%, slight differences in bacterial populations were observed in both the center and the surface portions. Taken together, our results suggest that environmental and processing variables of cheese manufacturing including pasteurization, starter, ripening conditions are important factors influencing the bacterial diversity in cheese and they can be used to alter nutrient profiles and metabolism and the flavor during ripening.

비살균 원유로 제조된 다양한 Gouda 치즈의 미생물 안전성

본 연구에서는 비살균 원유로 제조되고 숙성실에서 60일 이상 숙성된 7가지의 다양한 Gouda 치즈의 미생물학적 안전성을 실험적으로 검증하기 위해서 저장기간 동안에 다양한 미생물학적 변화를 조사하였다. Cheese 1과 2는 전통적인 비살균 Godua 치즈에 있어서는 60일 저장기간 동안 Salmonella spp.는 전혀 검출되지 않았으며, E. coli는 20 day부터는 검출되지 않았다. 대장균군은 Cheese 1에서 40 day부터 검출되지 않았지만, Cheese 2에서는 60 day까지 검출되었다. Cheese1과 Cheese 2는 비살균 Gouda 치즈이기에 약간의 차이는 있었지만 전반적으로 비슷한 경향을 보였다. Cheese 3(원유에 인위적으로 Salmonella spp.를 오염시킨 후 제조된 비살균 Gouda 치즈), Cheese 4(Cheese 3에서 kefir에서 분리한 DH5 유산균 첨가)와 Cheese 5(Cheese 3에서 kefir에서 분리한 DN1 유산균 첨가)에 있어서는 60일 저장기간 동안 Salmonella spp.의 저해가 관찰되었다. 특히 Cheese 4와 Cheese 5에 추가적으로 첨가된 Kefir에서 분리한 유산균 DH5와 DN1은 Cheese 3보다 유의적으로 Salmonella spp.의 저해를 보였다. Cheese 6(유산균첨가 없이 제조된 비살균 Gouda 치즈)에서는 저장기간이 길어질수록 유산균수가 다른 Cheese들에 비해서 유의적으로 낮게 나타났다. 그리고 Cheese 7(살균한 원유로 제조한 전통적인 Gouda 치즈)에 있어서는 대장균 및 대장균군, Salmonella ssp.는 거의 검출되지 않았고, 유산균은 다른 Cheese들보다 약간 높게 나타났다. 60일 숙성된 Cheese 1부터 Cheese 7까지의 모든 샘플에 대한 Listeria monocytogenes, Staphylococcus aureus, Clostridium perfringens, E. coli O157:H7 검사에서 모두 음성을 보였다. 향후 kefir에서 분리한 유산균 DH5와 DN1의 비살균 원유를 이용한 숙성치즈의 제조에 관한 연구가 필요하겠다. 본 연구에서 Salmonella spp.를 인위적으로 접종한 Cheese 4와 5에서 보여준 Salmonella spp.의 저해 효과는 비살균 원유를 이용한 숙성치즈의 제조에 보다 큰 안전성을 부여할 것이라 사료된다.

비살균 원유로 제조된 다양한 Gouda 치즈의 관능평가

비살균 원유로 제조된 다양한 Gouda 치즈의 관능평가

Kinetic models of quality parameters of spreadable processed Gouda cheese during storage

The aim of the study was to prepare mathematical models based on the Arrhenius equation as predictive tools for the assessment of changes in quality parameters during the storage of spreadable Gouda cheese at temperatures of 8, 20 and 30 °C. The activation energy value and the chemical reaction rate constant enabled the construction of kinetic models, which helped to estimate the direction and rate of changes. Moreover, the activation energy (Ea) of the quality parameters was used to determine the sequence of their vulnerability during storage. The value of activation energy corresponding to temperature changes resulted in the following order of susceptibility of the quality parameters: ΔC > ΔE ≈ water activity > texture parameters > pH > colour > sensory parameters > rheological parameters. The research showed limited applicability of the mathematical models for estimation of quality parameters referring to spreadable processed Gouda cheese.

Antioxidant activity, fatty acids characterization and oxidative stability of Gouda cheese fortified with mango (Mangifera indica L.) kernel fat.

Effect of mango kernel fat (MKF) on antioxidant characteristics and lipolysis of Gouda cheese was investigated. Milk fat (3.5%) was partially replaced with MKF i.e. 5, 10, 15 and 20% concentrations (T1, T2, T3 and T4). Cheese prepared from 100% milk fat served as control. Cheese samples were ripened for 90days at 6±1°C and analysed at 0, 45 and 90days of ripening. Total phenolic contents of control, T1, T2, T3 and T4 were 14±0.35, 129±0.75, 188±2.52, 267±10.61 and 391±8.46mg GAE/g. Total flavonoid content of control, T1, T2, T3 and T4 were 0.22±0.03, 1.47±0.09, 3.62±0.15, 5.88±0.35, 8.29±0.63mg quercetin equivalent/ml. DPPH free radical scavenging activity of control and experimental samples increased throughout the ripening period. DPPH free radicals scavenging activity of 90days old control, T1, T2, T3 and T4 were 16.38±0.0.26e, 30.47±0.64d, 68.62±0.91c, 73.29±0.85b, 92.61±1.44a%. HPLC characterization revealed the existence of mangiferin, caffeic acid, catechin, quercetin and chlorogenic acid in MKF fortified Gouda cheese. Fortification of MKF increased the concentration of C18:1, C18:2 and C18:3 in cheese. The concentration of C18:1, C18:2 and C18:3 in control were 24.55±0.95, 1.76±0.09 and 0.31±0.02%. While, the concentration of C18:1, C18:2 and C18:3 in T4 were 30.11±1.34, 2.79±2.79 and 0.92±0.11%. MKF fortified Gouda cheese had better oxidative stability and sensory characteristics. These results evidenced that antioxidant capacity, unsaturated fatty acids and oxidative stability of Gouda cheese can be improved with MKF.

Outbreak of Escherichia coli O157:H7 Infections Linked to Aged Raw Milk Gouda Cheese, Canada, 2013

Between 12 July and 29 September 2013, 29 individuals in five Canadian provinces became ill following infection with the same strain of Escherichia coli O157:H7 as defined by molecular typing results. Five case patients were hospitalized, and one died. Twenty-six case patients (90%) reported eating Gouda cheese originating from a dairy plant in British Columbia. All of the 22 case patients with sufficient product details available reported consuming Gouda cheese made with raw milk; this cheese had been produced between March and July 2013 and was aged for a minimum of 60 days. The outbreak strain was isolated from the implicated Gouda cheese, including one core sample obtained from an intact cheese wheel 83 days after production. The findings indicate that raw milk was the primary source of the E. coli O157:H7, which persisted through production and the minimum 60-day aging period. This outbreak is the third caused by E. coli O157:H7 traced to Gouda cheese made with raw milk in North America. These findings provide further evidence that a 60-day ripening period cannot ensure die-off of pathogens that might be present in raw milk Gouda cheese after production and have triggered an evaluation of processing conditions, physicochemical parameters, and options to mitigate the risk of E. coli O157:H7 infection associated with raw milk Gouda cheese produced in Canada.

Sensory and chemical properties of Gouda cheese

Gouda cheese is a washed-curd cheese that is traditionally produced from bovine milk and brined before ripening for 1 to 20 mo. In response to domestic and international demand, US production of Gouda cheese has more than doubled in recent years. An understanding of the chemical and sensory properties of Gouda cheese can help manufacturers create desirable products. The objective of this study was to determine the chemical and sensory properties of Gouda cheeses. Commercial Gouda cheeses (n = 36; 3 mo to 5 yr; domestic and international) were obtained in duplicate lots. Volatile compounds were extracted by solid-phase microextraction and analyzed by gas chromatography-olfactometry and gas chromatography-mass spectrometry. Composition analyses included pH, proximate analysis, salt content, organic acid analysis by HPLC, and color. Flavor and texture properties were determined by descriptive sensory analysis. Focus groups were conducted to document US consumer perception followed by consumer acceptance testing (n = 149) with selected cheeses. Ninety aroma-active compounds in Gouda cheeses were detected by solid-phase microextraction/gas chromatography-olfactometry. Key aroma-active volatile compounds included diacetyl, 2- and 3-methylbutanal, 2-methylpropanal, methional, ethyl butyrate, acetic acid, butyric acid, homofuraneol, δ-decalactone, and 2-isobutyl-3-methoxypyrazine. Aged cheeses had higher organic acid concentrations, higher fat and salt contents, and lower moisture content than younger cheeses. Younger cheeses were characterized by milky, whey, sour aromatic, and diacetyl flavors, whereas aged cheeses were characterized by fruity, caramel, malty/nutty, and brothy flavors. International cheeses were differentiated by the presence of low intensities of cowy/barny and grassy flavors. Younger cheeses were characterized by higher intensities of smoothness and mouth coating, whereas aged cheeses were characterized by higher intensities of fracture and firmness. American consumers used Gouda cheese in numerous applications and stated that packaging appeal, quality, and age were more important than country of origin or nutrition when purchasing Gouda cheeses. Young and medium US cheeses ≤6 mo were most liked by US consumers. Three distinct consumer segments were identified with distinct preferences for cheese flavor and texture. Findings from this study establish key differences in Gouda cheese regarding age and origin and identify US consumer desires for this cheese category.

Novel consortium of Klebsiella variicola and Lactobacillus species enhances the functional potential of fermented dairy products by increasing the availability of branched-chain amino acids and the amount of distinctive volatiles.

Identify novel bacterial taxa that could increase the availability of branched-chain amino acids and the amount of distinctive volatiles during skim milk fermentation. We recovered 344 bacterial isolates from stool samples of healthy and breastfed infants. Five were selected based on their ability to produce branched-chain amino acids. Three strains were identified as Escherichia coli, one as Klebsiella pneumoniae and other as Klebsiella variicola by molecular and biochemical methods. HPLC and solid-phase microextraction with GC-MS were used for the determination of free amino acids and volatile compounds respectively. The consortium formed by K. variicola and four Lactobacillus species showed the highest production of Leu and Ile in skim milk fermentation. In addition, the production of volatile compounds, such as acetoin, ethanol, 2-nonanone, and acetic, hexanoic and octanoic acids, increased in comparison to commercial yogurt, Emmental and Gouda cheese. Also, distinctive volatiles, such as 2,3-butanediol, 4-methyl-2- hexanone and octanol, were identified. The use of K. variicola in combination with probiotic Lactobacillus species enhances the availability of Leu and Ile and the amount of distinctive volatiles during skim milk fermentation. The identified consortium increases the functional potential of fermented dairy products.

Factors that inhibit growth of Listeria monocytogenes in nature-ripened Gouda cheese: A major role for undissociated lactic acid

In this study, factors relevant to nature-ripened Gouda cheese were evaluated for their potential to inhibit growth of Listeria monocytogenes. Factors included water activity, pH, undissociated acetic and lactic acid, diacetyl, free fatty acids, lactoferrin, nitrate, nitrite and nisin. In addition, the effect of temperature was evaluated. For each factor, the actual concentrations and values relevant to Gouda cheese were obtained and the inhibitory effect of these individual factors on growth of L. monocytogenes was assessed. This evaluation revealed that undissociated lactic acid is the most important factor for growth inhibition of L. monocytogenes in Gouda cheese and that, additionally, low water activity as present in the cheese rind and after prolonged ripening times can also cause full growth inhibition. Gouda cheeses have a typical total lactic acid content of 1.47% w/w. In a 2-week old Gouda cheese, with a pH value of 5.25 and a moisture content of 42% w/w, the concentration of undissociated lactic acid in the water phase is 10.9 mM. Growth of L. monocytogenes is not supported when the undissociated lactic acid concentration is >6.35 mM. Concentrations of undissociated lactic acid in the water phase of Gouda cheese will be higher than this value when the total lactic acid content is >0.86% w/w at a pH < 5.25 (relevant to young Gouda cheese), or >1.26% w/w at a pH < 5.50 for mature Gouda cheese (moisture content of 35% w/w). This study underlines the importance of undissociated lactic acid as growth inhibitor for L. monocytogenes in Gouda cheese.

Measuring temporal liking simultaneously to Temporal Dominance of Sensations in several intakes. An application to Gouda cheeses in 6 Europeans countries

The idea of having untrained consumers performing Temporal Dominance of Sensations (TDS) and dynamic liking in the same session was recently introduced (Thomas, van der Stelt, Prokop, Lawlor, & Schlich, 2016). In the present study, a variation of the data acquisition protocol was done, aiming to record TDS and liking simultaneously on the same screen in a single session during multiple product intakes. This method, called Simultaneous Temporal Drivers of Liking (S-TDL), was used to describe samples of Gouda cheese in an international experiment.To test this idea, consumers from six European countries (n=667) assessed 4 Gouda cheeses with different ages and fat contents during one sensory evaluation session. Ten sensory attributes and a 9-point hedonic scale were presented simultaneously on the computer screen. While performing TDS, consumers could reassess their liking score as often as they wanted. This new type of sensory data was coded by individual average liking scores while a given attribute was perceived as dominant (Liking While Dominant; LWD).Although significant differences in preference were observed among countries, there were global preferences for a longer dominance of melting, fatty and tender textures. The cheese flavour attribute was the best positive TDL, whereas bitter was a strong negative TDL. A cluster analysis of the 667 consumers identified three significant liking clusters, each with different most and least preferred samples. For the TDL computation by cluster, significant specific TDL were observed. These results showed the importance of overall liking segmentation before TDL analysis to determine which attributes should have a longer dominance duration in order to please specific consumer targets.

Contribution of the novel sulfur-producing adjunct Lactobacillus nodensis to flavor development in Gouda cheese

We assessed the efficacy of Lactobacillus nodensis CSK964 as an adjunct culture in Gouda cheese under various industrial conditions. We set up 4 different systems: a direct vat inoculum with and without adjunct using the calf rennet Kalase, and an undefined bulk starter culture with and without adjunct using the microbial rennet Milase (both rennets from CSK Food Enrichment, Ede, the Netherlands). During ripening, we subjected the cheeses to the following analyses: viability of starter and adjunct cells, composition, proteolysis, and flavor development by detection of sulfur compounds and descriptive sensory analysis. In general, the presence of Lb. nodensis increased secondary proteolysis and influenced cheese flavor, particularly in relation to volatile sulfur compounds; hydrogen sulfide and methanethiol were present in higher abundances in cheeses containing Lb. nodensis. The primary starter also influenced the range of volatile sulfur compounds produced. Methanethiol and dimethyl disulfide were more abundant in the nisin-producing direct vat inoculum cheese with adjunct; hydrogen sulfide was more prevalent when bulk starter culture was used with Lb. nodensis. Sensory analysis revealed that the direct vat inoculum cheese with adjunct scored significantly better in terms of smell and taste than the direct vat inoculum cheese without adjunct and lacked the dominant sulfur flavors of the bulk starter cheese with adjunct. Subsequent analysis using lead acetate paper and modified motility broth as indicators of hydrogen sulfide production confirmed that Lb. nodensis produced hydrogen sulfide in broth and in the cheese matrix. This study suggests that the inclusion of Lb. nodensis as an adjunct culture can significantly alter the flavor profile of the final cheese. However, the selection of a suitable primary starter is imperative to ensure a desirable product.

Characteristics of Gouda Cheese Supplemented with Chili Pepper Extract Microcapsules.

In this study, the physicochemical and sensory properties of Gouda cheese supplemented with microcapsules of chili pepper extract were evaluated. Microcapsules of pepper extract were prepared by coacervation technique using gum acacia-gelatin wall and chili pepper oil core. Changes in pH, lactic acid bacteria (LAB) population, and free amino acid (FAA) content after supplementation of Gouda cheese with chili pepper capsules were monitored during ripening. Texture and sensory characteristics of the Gouda cheese ripened for 6 months were evaluated. The supplementation of pepper extract microcapsules (0.5% or 1%, w/w) did not influence the pH values and LAB content of the Gouda cheese (p<0.05) during the ripening period. While the content of total FAA increased with the ripening process in all the cheese groups (p<0.05), no significant difference (p<0.05) in the content of total FAA was observed among the sample groups at each time point. The addition of pepper extract microcapsules (1%, w/w) to Gouda cheese significantly decreased hardness (p<0.05) and negatively affected sensory attributes in terms of taste and texture (p<0.05). The results demonstrated that supplementation with 0.5% pepper extract microcapsules could provide additional bioactive ingredients, along with maintenance of the quality of Gouda cheese.

The role of immobilized rennet on carbon cloth in flavor development during ripening of Gouda cheese.

Rennet-free Gouda (RFG) cheese was prepared to investigate the influence of rennet on the non-volatile and volatile profiles of cheese and was characterized by HPLC and GC/MS analyses. Chymosin, a major protease in rennet, was immobilized onto oxidized and chemically modified carbon cloth. The chymosin immobilization efficiency was 60.4%, and the milk-clotting activity used as an index of the stability of the immobilized chymosin decreased by around 20% in 2 weeks. However, the activity was maintained at 70-80% from 2 weeks to 32 weeks and was more stable than that of chymosin solution alone. Non-volatile (organic acids) and volatile profiles of the RFG cheese and rennet-containing normal Gouda cheese were not significantly different during ripening with a few exceptions. Therefore, it can be concluded that cheese flavor is developed by lactic acid fermentation, irrespective of the presence of rennet.

착유방식이 목장형 유가공으로 제조된 고다치즈의 품질 특성에 미치는 영향

This investigation was carried out to study effects of different milking systems on the characteristics of Gouda cheese produced at farmstead milk-processing plants. In the first study, raw milk was collected from automatic milking system and conventional milking system farms, and Gouda cheeses were prepared under the same conditions. After 6 months of aging, the chemical composition was analyzed and free fatty acid (FFA) analysis and sensory evaluation were carried out on the products. In the second study, Gouda cheese samples were collected from seven farmstead milk-processing plants and the chemical composition and texture profile analysis were evaluated. No significant differences were found in the chemical composition of Gouda cheese according to different milking systems or different farms except crude ash. FFA analysis showed significant differences among farms, but sensory evaluation showed no significant differences. No significant differences were observed in FFA content and sensory assessment of different milking systems. Texture profile analysis revealed that there were significant differences in each cheese made at different farm plants, but there were no differences when different milking systems were used.

Application of a puffer fish skin gelatin film containing Moringa oleifera Lam. leaf extract to the packaging of Gouda cheese.

This study aims to develop a puffer fish skin gelatin (PSG) film that contains Moringa oleifera Lam. leaf extract (ME) as a new biodegradable film. With the increase in ME concentration, the tensile strength and elongation at break of the PSG film increased, whereas the oxygen permeability and water vapor permeability decreased. In addition, the PSG film with ME exhibited antimicrobial activity against Listeria monocytogenes and antioxidant activity. To apply the ME-containing PSG film to food packaging, Gouda cheese was wrapped with the ME-containing PSG film. During storage, the cheese packaging with the ME-containing PSG film effectively inhibited the microbial growth and retarded the lipid oxidation of cheese compared with the control sample. Thus, the ME-containing PSG film can be used as an antimicrobial and antioxidative packaging material to improve the quality of food products.

Characterization of the Microbial Diversity and Chemical Composition of Gouda Cheese Made by Potential Probiotic Strains as an Adjunct Starter Culture.

This study characterized the microbial diversity and chemical properties of Gouda cheese made by probiotics during ripening periods. Lactobacillus plantarum H4 (H4) and Lactobacillus fermentum H9 (H9), which demonstrate probiotic properties and bioactivity, were used as adjunct starter cultures. Gouda cheese made with H4 (GCP1) and H9 (GCP2) demonstrated the highest production of formic acid and propionic acid, respectively. Moreover, the bacterial diversity, including richness and evenness of nonstarter lactic acid bacteria (NSLAB), increased in probiotic cheeses. Specifically, Lactobacillus, Leuconostoc, and Streptococcaceae were present at higher concentrations in probiotic cheeses than in control Gouda cheese (GCC). The proportion of H4 in GCP1 increased and culminated at 1.76%, whereas H9 in GCP2 decreased during ripening. Peptide profiles were altered by the addition of probiotics and included various bioactive peptides. In particular, three peptide fragments are newly detected. Therefore, Gouda cheese could be used as an effective probiotic carrier for H4 and H9.

Optimising Cheese Brining Times

In this article we detail the work conducted during MISG2014 on the brining of Gouda cheese for the Fonterra Cooperative Group. We consider three different mathematical models that aim to predict the salt content of cheese post-brining. The first is a diffusion model that accounts for the interstitial volume that is available for salt and water transport within the cheese. It predicts moisture content that agrees closely with data provided by Fonterra, and we show how modifications to the salt diffusivity and partial molar volume can improve the accuracy of the salt content predictions. The second model considers the moisture in the cheese to be in two phases---free moisture that contributes to the porosity of the cheese and is accessible to salt diffusion, and water that is bound by the cheese protein. The third model, referred to here as the salt-uptake model, is a reaction-diffusion model that considers salt being bound to the cheese matrix as it diffuses through the cheese. More work is required on this model to be able to draw conclusions regarding the cheese brining process. References P. W. Atkins. Physical Chemistry . Oxford University Press, 4th edition, 1990. G. Aylward and T. Findlay. SI Chemical data . John Wiley and Sons, 1974. D. A. G. Bruggeman. Calculation of the various physical constants of heterogeneous substances. I: Dielectric constants and conductivities of mixtures of isotropic substances. Annalen der Physik , 25:636–664, 1935. doi:10.1002/andp.19354160705 . G. Carey, N. Fowkes, A. Staelens, , and A. Pardhanani. A class of coupled nonlinear reaction diffusion models exhibiting fingering. Journal of Computational and Applied Mathematics , 166(1), 2004. doi:10.1016/j.cam.2003.09.037 . R. Datta and S. A. Vilekar. The continuum mechanical theory of multicomponent diffusion in fluid mixtures. Chemical Engineering Science , 65:5976–5989, 2010. doi:10.1016/j.ces.2010.08.022 . C. J. D. Fell and H. Hutchison. Diffusion coefficients for sodium and potassium chlorides in water at elevated temperatures. Journal of Chemical and Engineering Data , 16:427–429, 1971. doi:10.1021/je60051a005 . Fonterra Co-Operative Group. Personal communication. 2014. T. J. Geurts, P. Walstra, , and H. Mulder. Transport of salt and water during salting of cheese. 1: Analysis of the processes involved. Netherlands Milk and Dairy Journal , 28:102–129, 1974. T. P. Guinee. Salting and the role of salt in cheese. International Journal of Dairy Technology , 57(2):99–109, 2004. doi:10.1017/S0022112003005512 . T. P. Guinee and P. Fox. Sodium chloride and moisture changes in romano–type cheese during salting. Journal of Dairy Research , 50:511–518, 1983. doi:10.1017/S002202990003274X . J. A. Luna and M. S. Chavez. Mathematical model for water diffusion during brining of hard and semi–hard cheese. Journal of Food Science , 57:55–58, 1992. doi:10.1111/j.1365-2621.1992.tb05423.x . K. Mandl, R. W. Hartel, and W. Wendorff. Effects of moisture and salt migration on cheese firmness in cheese–in–sausage products. Journal of Food Engineering , 91:164–172, 2009. doi:10.1016/j.jfoodeng.2008.08.022 . MATLAB. version 8.1 (R2013a) . The MathWorks Inc., Natick, Massachusetts, 2013. W. Messens, K. Dewettinck, and A. Huyghebaert. Transport of sodium chloride and water in gouda cheese as affected by high–pressure brining. International Dairy Journal , 9:569–576, 1999. doi:10.1016/S0958-6946(99)00126-0 . M. R. Payne and K. R. Morison. A multi–component approach to salt and water diffusion in cheese. International Dairy Journal , 9:887–894, 1999. doi:10.1016/S0958-6946(99)00157-0 . M. Turhan and G. Kaletunc. Modeling of salt diffusion in white cheese during long–term brining. Journal of Food Science , 57:1082–1085, 1992. doi:10.1111/j.1365-2621.1992.tb11269.x . H. Weingartner. Self–diffusion in liquid water. A reassessment. Zeitschrift fur Physikalische Chemie , 132:129–149, 1982. doi:10.1524/zpch.1982.132.2.129 .

How NaCl and water content determine water activity during ripening of Gouda cheese, and the predicted effect on inhibition of Listeria monocytogenes

This study describes the diffusion of NaCl and water in Gouda cheese during brining and ripening. Furthermore, we established water activity as a function of the NaCl-in-moisture content in Gouda cheese during ripening. We determined NaCl content, water content, and water activity in block-type Gouda cheeses that were brined for 3.8d and foil-ripened for a period of 26 wk, and in wheel-type Gouda cheeses that were brined for 0.33, 2.1, or 8.9d and subsequently nature-ripened for a period of 26 wk. The calculated diffusion coefficients of NaCl during brining were 3.6·10−10 m2s−1 in the block-type Gouda cheeses and 3.5·10−10 m2s−1 in the wheel-type Gouda cheeses. Immediately after brining, gradients of NaCl and water were observed throughout both types of cheese. During ripening, these gradients disappeared, except for the water gradient in nature-ripened cheeses. An empirical model was derived for Gouda cheese, in which water activity is expressed as a function of the NaCl-in-moisture content, as established for different brining times, locations and ripening times. Moreover, the effect of reduced water activity on inhibition of growth of Listeria monocytogenes in Gouda cheese was calculated. In addition to the presence of lactate and a pH of 5.2 to 5.3, the reduced water activity as seen in Gouda cheese can substantially contribute to inhibition of microbial growth and even to inactivation when cheeses are brined and ripened for extended times and subjected to nature-ripening.

Conjugated linoleic acid of dairy foods is affected by cows’ feeding system and processing of milk

The distribution of conjugated linoleic acid (CLA) in dairy products commercially available in Chile is poorly understood. This study aimed to assess the content of CLA in dairy cow products from Chile and the effect of processing fresh milk into dairy products. Samples of raw milk were categorized into two groups based on the animal feeding system utilized by the dairy farm: 1) grazing based systems (Los Lagos region); and 2) housing systems using total mixed ration (TMR) diets (Los Angeles region). Simultaneously, commercial samples of condensed milk, powdered milk, butter and Gouda cheese were analyzed. Furthermore, samples of raw milk and processed products (powdered and sweetened condensed milk) were also analyzed. Dairy farms based on grazing systems had higher levels of CLA in raw milk than TMR farms. In addition, average values of CLA were 1.72 g 100 g−1 of total fatty acids, in spring milk in the Los Lagos region, and 0.42 g 100 g−1 in summer milk, in the Los Angeles region. Similarly, the CLA content of dairy products was higher than that of raw milk. Milk processing affected the transferring of CLA from fresh milk into the final products. Sweetened condensed milk presented lower CLA values than raw and powdered milk. In conclusion, this study indicates the importance of the production systems to the CLA content as well as the effects of milk processing into dairy products. To sum up, more research is needed to elucidate the exact effect of the processing conditions of dairy products on the CLA content.

Minimal inhibitory concentrations of undissociated lactic, acetic, citric and propionic acid for Listeria monocytogenes under conditions relevant to cheese

Minimal inhibitory concentrations (MICs) of undissociated lactic acid were determined for six different Listeria monocytogenes strains at 30 °C and in a pH range of 4.2–5.8. Small increments in pH and acid concentrations were used to accurately establish the growth/no growth limits of L. monocytogenes for these acids. The MICs of undissociated lactic acid in the pH range of 5.2–5.8 were generally higher than at pH 4.6 for the different L. monocytogenes strains. The average MIC of undissociated lactic acid was 5.0 (SD 1.5) mM in the pH range 5.2–5.6, which is relevant to Gouda cheese. Significant differences in MICs of undissociated lactic acid were found between strains of L. monocytogenes at a given pH, with a maximum observed level of 9.0 mM. Variations in MICs were mostly due to strain variation. In the pH range 5.2–5.6, the MICs of undissociated lactic acid were not significantly different at 12 °C and 30 °C. The average MICs of undissociated acetic acid, citric acid, and propionic acid were 19.0 (SD 6.5) mM, 3.8 (SD 0.9) mM, and 11.0 (SD 6.3) mM, respectively, for the six L. monocytogenes strains tested in the pH range 5.2–5.6. Variations in MICs of these organic acids for L. monocytogenes were also mostly due to strain variation. The generated data contribute to improved predictions of growth/no growth of L. monocytogenes in cheese and other foods containing these organic acids.