Evaluation of false positive results in microbial inhibitor tests for screening antibiotics in goat milk

Tesis por compendioGoat milk is primarily destined for the production of fermented products, in particular cheese. Therefore, the control of antibiotic residues in milk is of great importance, since these could have negative repercussions on technological properties of the milk as well as on the health of consumers. In milk quality control programs, microbial inhibitor tests are widely applied to detect antibiotics during the screening stage. However, tests are non-specific and may be affected by substances other than antimicrobials which could inhibit the growth of the test micro-organism, causing false positive results. The aim of this thesis was to evaluate the interference, related to the presence of different contaminants in goat milk, on the response of microbial inhibitor tests commonly used in Spain to detect antibiotics (BRT MRL, Delvotest SP-NT MCS and Eclipse 100 tests). The influence of the physicochemical characteristics of goat milk on the false positive outcomes in microbial screening tests was also investigated. The suitability of microbial inhibitor tests for screening antibiotics in colostrum secretions was studied by analysing antibiotic-free colostrum and milk samples from forty-three Murciano-Granadina goats, collected every 12 hours during the first week post-partum. Microbial inhibitor tests were not suitable for the analysis of goat colostrum because they presented a high percentage of doubtful and positive results (up 37.2% in the 36 hours after partum). To evaluate the effect of caprine colostrum on the microbial test response, antimicrobial-free goat milk spiked with different concentrations of colostrum was analysed to calculate the inhibitory concentrations producing 5% of positive results. The highest interferences were obtained for the addition of colostrum from 12 to 24 hours post-partum and the colostrum concentrations producing 5% positive results were between 5.1 and 34.6%. The BRT MRL was the test the most affected. In another study, the interference of detergents and disinfectants used for the cleaning of milking equipment and milk storage tanks of dairy farms was investigated. Antimicrobial-free goat milk was spiked with eight concentrations of different cleaning products (5 acid, 5 alkaline, 5 domestic washing-up liquids, and 1 disinfectant) and analysed using microbial screening tests. The presence of acid detergent and disinfectant based on sodium hypochlorite in goat milk did not affect the microbial test response. However, alkaline detergents at concentrations ≥ 1 ml/l could lead to false positive results in microbial inhibitor tests (up to 16.7%) and from 4 ml/l on 100% positive results were obtained. Regarding the products used for home use, and those used on farms and small size dairies, washing-up liquid containing sodium laureth sulphate and ethanol had the greatest effects on microbial inhibitor tests, even starting from a relatively low concentration (1 ml/l). On the other hand, the presence of a relatively low concentration of detergents in goat milk (0.5 ml/l) slightly modified the detection capability of the microbial inhibitor tests for amoxicillin, ampicillin, benzylpenicillin, and cloxacillin, although the detection of these drugs at MRL (safe level) was not compromised. Antiparasitic agent residues in goat milk could be another possible cause of false positive results in microbial screening tests. An in vitro study to evaluate the effect of seven parasiticides commonly used in dairy goats was carried out. Further two studies, where albendazole and ivermectin were applied to two groups of dairy goats in lactation were performed. It should be noted that the parasiticide ivermectin is banned for the treatment of animals producing milk for human consumption, although its inclusion in this study was considered interesting to understand the potential effect of their residues in milk, in the event the practice was performed illegally. In the in vitro study, raw antibiotic-free milk from goats was spiked individually with eight different concentrations of albendazole, closantel, diclazuril, febendazole, levamisole, diazinon, and ivermectin. The microbial inhibitor test results showed a great variability according to the test and the drug under study. Of the tests considered, the BRT MRL test was the most sensitive to antiparasitic agents, with the lowest concentrations of antiparasitic agent causing 5, 10, and 50% of positive results. Generally, closantel and diazinon were the antiparasitic agents that produced higher interferences in all tests, since low concentrations already resulted in positive results, while only higher concentrations of diclazuril and ivermectin showed an inhibitory effect. To evaluate the effect of albendazole residues on the microbial inhibitor test response, eighteen healthy Murciano-Granadina goats in mid-lactation were treated with a single oral administration of the commercially available albendazole registered for dairy sheep (7.5 mg/kg b.w. of active compound) with a withdrawal period of 4 days for milk production in ovine. Albendazole and its metabolite residues in goat milk after under cascade treatment were not detected above MRL from the third day post-administration. However, a high occurrence of non-compliant results was obtained for the BRT MRL test during the first six days after treatment, suggesting that factors related to the albendazole application other than the drug concentration are able to affect the microbial inhibitor test response in some cases. Regarding the ivermectin study, twenty-eight Murciano-Granadina goats infested with Sarcoptes scabiei var. caprae were treated with a subcutaneous injection of ivermectin (200 μg/kg b.w.), with a second dose applied seven days after the first treatment. Drug residues in goat milk were recorded during the first fifteen days of the experiment with concentrations ranging from 8.13 to 24.25 ng/ml. In addition, all the microbial screening tests seem to be affected by the ivermectin treatment, with BRT MRL the most affected (20%) compared with Delvotest SP-NT MCS and Eclipse 100 (6.6 and 5.7%, respectively). These positive results cannot be associated with the ivermectin concentration in goat milk, as the concentrations measured were lower than the inhibitory concentrations as reported in a previous in vitro study for these microbial tests. Thus, as suggested by some authors, interferences could be related to changes or alterations caused by the application of the parasiticide agent or by the parasitic disease itself, which could affect the immune response of the animals favouring the presence of inhibitory substances in milk. The study of the effect of the goat milk composition on the specificity (rate of false positive results) of microbial inhibitor tests for screening antibiotics was also considered. Thus, individual goat milk samples (n=200) were analysed by microbial inhibitor tests using both visual and instrumental classification of the test results. The highest specificity values were obtained for the instrumental interpretation of the test results (94-99% vs 90-96%) due to the occurrence of samples with intermediate colorations (green-yellow, yellow-blue) making the visual classification more difficult and subjective. A relation was found between positive results in BRT MRL and Eclipse 100 tests and an elevated fat content in the goat milk. Positive outcomes in Eclipse 100 were associated with the butyric acid concentration in the milk. Further, the Delvotest SP-NT MCS test response was affected by elevated pH values, high lactoferrrin and myristoleic acid concentrations in the goat milk. This percentage of positive results could be minimized by a pre-treatment prior to microbial inhibitor test analysis, such as fat removal by centrifugation (3,100 g for 10 min at 4 ºC) and/or heating (80 ºC for 10 min). Undoubtedly, improvements on the specificity of the microbial inhibitor tests for screening antibiotics in goat milk are desirable to avoid the destruction of milk compliant for human due to the occurrence of false positive results. The related financial losses affect farmers and dairies. However, it should be noted that the presence of contaminants in goat milk could be avoided by applying good farming practices designed to ensure that milk is obtained from healthy animals under proper hygienic conditions so ensuring the food safety of goat milk and related dairy products.Romero Rueda, T. (2015). Evaluation of false positive results in microbial inhibitor tests for screening antibiotics in goat milk [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/48552TESISCompendi

APTITUD AL ORDEÑO MECÁNICO EN LA OVEJA GUIRRA: LECHE CISTERNAL Y ALVEOLAR

Se ha estudiado la aptitud al ordeño mecánico en la oveja de la raza Guirra, centrando el estudio en las fracciones cisternal y alveolar. Se concluye que el fraccionamiento en esta raza es similar al que presentan otras razas autóctonas españolas.Romero Rueda, T. (2009). APTITUD AL ORDEÑO MECÁNICO EN LA OVEJA GUIRRA: LECHE CISTERNAL Y ALVEOLAR. http://hdl.handle.net/10251/14083Archivo delegad

Energy balance data from lactating dairy goats offered total mixed diets

[EN] The objective of the study was to develop a univariate model for analyzing energy balance data from lactating goats at mid lactation and determine maintenance requirements and partial efficiencies of energy utilization. Energy balance data from eight studies involving lactating Murciano-Granadina goats fed total mixed diets, which accounted for a variation in metabolizable energy (MEI) intake, milk energy output (EI), and tissue energy balance, were used. The database included records obtained by indirect calorimetry. Data were adjusted with a mixed model that included the study as a random effect. Then, two multivariate linear models were obtained: metabolizable and net energy models. The metabolizable model was MEI=ß0+ß2E1+ß3Tg+ß4T1+¿ and the net energy model was E1=ß0+ß1MEI+ß2Tg+ß3T1+¿; where ß0, ß1, ß2 and ß3 were the parameters, Tg was tissue energy retention and Tl the milk energy derived from body stores. For a better fitted proposed model, net energy for maintenance (NEm) was 283 kJ/kg of Body Weight 0.75 (BW) per day, and the efficiency of utilization of ME for lactation (k1), body weight gain (kg) and body tissue mobilization for milk production (kt) were 62%, 83% and 78%, respectively. Maintenance requirements and partial efficiencies for milk production and tissue energy mobilization were similar to the values proposed by INRA (2018). The increase in the efficiency of utilizing dietary energy for gain, compared with other feeding systems, was partially attributed to the stage of lactation, due to that goats were feeding at mid lactationFernández Martínez, CJ.; Romero Rueda, T. (2019). Energy balance data from lactating dairy goats offered total mixed diets. Open Journal of Animal Sciences (Online). 9(4):385-400. https://doi.org/10.4236/ojas.2019.94031S3854009

Detection of antibiotics in goats' milk: Comparison of different commercial microbial inhibitor tests developed for the testing of cows' milk

[EN] Nine microbial inhibitor tests validated for cows' milk (BR-AS Special, CMT-Copan Milk Test, Delvotest SP-NT, Delvotest T, Brilliant Black Reduction Test MRL, Charm Blue Yellow II, Charm CowSide II, Eclipse 100, Eclipse 3G) were applied to milk samples from 200 different individual goats. Interpretation of the results was based on visual and instrumental reading. Samples initially testing positive were retested and also tested after a milk pre-treatment (heat treatment, fat removal or fat removal followed by heat treatment). With instrumental reading, most microbial tests commonly used for bovine milk were suitable for goats' milk (specificity 95%), except for BR-AS Special, Charm Blue Yellow II and Delvotest SP-NT. However, visual reading of the results decreased the specificity, with 95% specificity only for CMT-Copan Milk Test, Eclipse 3G and Delvotest T. Fat removal followed by heat treatment proved the most appropriate milk treatment to reduce false positive results for almost all tests.This work forms part of the grant EEBB-I-13-06255 financed by the Ministry of Science and Innovation (Madrid, Spain). The authors are grateful to Analytik in MilchProduktions-und Vertriebs-GmbH, Charm Sciences Inc., DSM Food Specialties, ZEULAB S.L. for their technological support. The authors thank MCC-Vlaanderen and Comite du Lait for the assistance with milk quality and composition analysis and appreciate the cooperation of the commercial dairy goat farms: J. VanWaes (Zaffelare, BE), 't Eikenhof (Lokeren, BE) and 't Leenhof (Zele, BE).Romero Rueda, T.; Van Weyenberg, S.; Molina Pons, MP.; Reybroeck, W. (2016). Detection of antibiotics in goats' milk: Comparison of different commercial microbial inhibitor tests developed for the testing of cows' milk. International Dairy Journal. 62:39-42. https://doi.org/10.1016/j.idairyj.2016.07.004S39426

Interference of non-specific detergents in microbial inhibitor test results for screening antibiotics in goat s milk

[EN] Cleaning and disinfection of dairy equipment is essential to ensure the hygienic quality of milk. Occasionally, some farmers use washing-up liquids and disinfectants for home use, especially when cleaning procedures are carried out manually. Residues of detergents and disinfectants in milk may interfere with the response of microbial inhibitor tests used for screening antibiotics in milk. Therefore, the aim of this study was to evaluate the interference of non-specific detergents in screening tests (BRT MRL; Delvotest SP-NT MCS; Eclipse 100) for goat s milk. Twelve replicates of eight concentrations of five washing-up liquids (0 1%) and one disinfectant (0 1%) were analysed. The results showed that the presence of washing-up liquids at concentrations of ≥1 ml/l leads to positive results in microbial tests. In particular, the product containing sodium laureth sulphate and ethanol produced the largest number of positive outcomes. The presence of disinfectant based on sodium hypochlorite did not affect the test response. The detection capabilities of microbial inhibitor tests for penicillins were also studied in milk with and without cleaning products, calculating the dose response curve with eight concentrations of amoxicillin, ampicillin, benzylpenicillin and cloxacillin, respectively. The detection limits of the screening tests for penicillins were not modified substantially by the cleaning product based on sodium laureth sulphate and ethanol. Residues of cleaning agents in milk can be avoided when specific detergents and disinfectants for milking equipment are used and good cleaning practices are applied.This work forms part of the Project AGL 2009-11524 financed by the Ministry of Science and Innovation (Madrid, Spain).Romero Rueda, T.; Beltrán Martínez, MC.; Althaus, RL.; Molina Pons, MP. (2016). Interference of non-specific detergents in microbial inhibitor test results for screening antibiotics in goat s milk. Journal of Applied Animal Research. 45(1):159-163. https://doi.org/10.1080/09712119.2015.1129341S159163451Beltrán, M. C., Berruga, M. I., Molina, A., Althaus, R. L., & Molina, M. P. (2015). Performance of current microbial tests for screening antibiotics in sheep and goat milk. International Dairy Journal, 41, 13-15. doi:10.1016/j.idairyj.2014.09.007Carlsson, Å., Björck, L., & Persson, K. (1989). Lactoferrin and Lysozyme in Milk During Acute Mastitis and Their Inhibitory Effect in Delvotest P. Journal of Dairy Science, 72(12), 3166-3175. doi:10.3168/jds.s0022-0302(89)79475-3Dubeuf, J.-P., de A. Ruiz Morales, F., & Castel Genis, J. M. (2010). Initiatives and projects to promote the Mediterranean local cheeses and their relations to the development of livestock systems and activities. Small Ruminant Research, 93(2-3), 67-75. doi:10.1016/j.smallrumres.2010.03.001LÓOPEZ, M. B., JORDÁN, M. J., GRANADOS, M. V., FERNÁNDEZ, J. C., CASTILLO, M., & LAENCINA, J. (1999). Viscosity changes during rennet coagulation of Murciano-Granadina goat milk. International Journal of Dairy Technology, 52(3), 102-106. doi:10.1111/j.1471-0307.1999.tb02081.xMERIN, U., ROSENTHAL, I., BERNSTEIN, S., & POPEL, G. (1985). The effect of residues of detergents and detergents-sanitizers on the performance of antibiotic test and the organoleptic quality of milk. Le Lait, 65(649-650), 163-167. doi:10.1051/lait:1985649-65011Oh, D.-H., & Marshall, D. L. (1993). Antimicrobial activity of ethanol, glycerol monolaurate or lactic acid against Listeria monocytogenes. International Journal of Food Microbiology, 20(4), 239-246. doi:10.1016/0168-1605(93)90168-gPontefract, R. D. (1991). Bacterial Adherence: Its Consequences in Food Processing. Canadian Institute of Food Science and Technology Journal, 24(3-4), 113-117. doi:10.1016/s0315-5463(91)70033-3Romero, T., Beltrán, M. C., Althaus, R. L., & Molina, M. P. (2014). Detection of antibiotics in goat’s milk: effect of detergents on the response of microbial inhibitor tests. Journal of Dairy Research, 81(3), 372-377. doi:10.1017/s0022029914000259Romero, T., Beltrán, M. C., Pérez-Baena, I., Rodríguez, M., & Molina, M. P. (2014). Effect of the presence of colostrum on microbial screening methods for antibiotic detection in goats’ milk. Small Ruminant Research, 121(2-3), 376-381. doi:10.1016/j.smallrumres.2014.07.007ROMERO, T., BELTRÁN, M. C., REYBROECK, W., & MOLINA, M. P. (2015). Effect In Vitro of Antiparasitic Drugs on Microbial Inhibitor Test Responses for Screening Antibiotic Residues in Goat’s Milk. Journal of Food Protection, 78(9), 1756-1759. doi:10.4315/0362-028x.jfp-15-020Sierra, D., Sánchez, A., Contreras, A., Luengo, C., Corrales, J. C., Morales, C. T., … Gonzalo, C. (2009). Detection limits of four antimicrobial residue screening tests for β-lactams in goat’s milk. Journal of Dairy Science, 92(8), 3585-3591. doi:10.3168/jds.2008-1981Valladao, M., & Sandine, W. E. (1994). Quaternary Ammonium Compounds in Milk: Detection by Reverse-Phase High Performance Liquid Chromatography and Their Effect on Starter Growth. Journal of Dairy Science, 77(6), 1509-1514. doi:10.3168/jds.s0022-0302(94)77090-9Zeng, S. S., Escobar, E. N., & Brown-Crowder, I. (1996). Evaluation of screening tests for detection of antibiotic residues in goat milk. Small Ruminant Research, 21(2), 155-160. doi:10.1016/0921-4488(95)00822-

Drug residues in goat s milk after to the prophylactic use of antibiotics in intravaginal sponges for estrus synchronization

[EN] The aim of this study was to determine whether the prophylactic use of antibiotics in intravaginal sponges used for estrus synchronization in goats may result in the presence of inhibitors in milk and, therefore, of positive results by microbial screening tests. Ninetyeight Murciano-Granadina goats were used, divided into 7 groups of 14 animals. Intravaginal sponges were placed in 6 groups using 2 concentrations of 3 different antibiotics: doxycycline, oxytetracycline, and sulfathiazole- framycetin. The sponges of the control group were placed without antibiotics. Milk samples were collected daily until 7 d posttreatment and analyzed using 3 microbial tests. Positive samples were retested by specific receptor-binding assays to confirm the positive results. Vaginal status was evaluated by visual assessment of the external aspect of the sponges after removal. The microbial test response was not affected by either day posttreatment or dose of antibiotic used, except for oxytetracycline at the higher concentration. Moreover, no positive results were obtained using receptor-binding assays, suggesting that residues, if present in milk, did not exceed the regulatory (safety) levels established for these drugs. The occurrence of soiled sponges was higher in the control group. With respect to the dose of antibiotics used, no significant differences were found for the lower dose administered. However, a significant increase in the percentage of clean sponges was observed for the higher dose of doxycycline. We conclude that the prophylactic use of low doses of doxycycline, oxytetracycline, or sulfathiazole in intravaginal sponges used for synchronization of estrus helps to reduce clinical vaginitis in dairy goats and does not seem to be the cause of positive results in microbial inhibitor tests used to detect antibiotics in goat milk.This work is part of the AGL-2009-11524 Project funded by the Spanish Ministry of Science and Innovation (Madrid, Spain). The authors are grateful to the Diputacion de Castellon and UNISENSOR S.A (Angleur, Belgium) for their support.Romero Rueda, T.; Balado, J.; Althaus, RL.; Beltrán Martínez, MC.; Molina Pons, MP. (2016). Drug residues in goat s milk after to the prophylactic use of antibiotics in intravaginal sponges for estrus synchronization. Journal of Dairy Science. 99(1):141-145. https://doi.org/10.3168/jds.2015-10200S14114599

Alterations in Energy Partitioning and Methane Emissions in Murciano-Granadina Goats Fed Orange Leaves and Rice Straw as a Replacement for Beet Pulp and Barley Straw

[EN] Reducing methane emissions in ruminants with the recycling of agro-industrial by-products is of great importance today. Pruning waste from citrus trees is currently burned or incorporated into soil. Regarding rice straw, this waste is traditionally eliminated through controlled burning, releasing into the atmosphere large amounts of greenhouse gases as well. The aim of this study was to convert this recovered waste into a new animal feed capable of reducing methane emissions in ruminants. The interest in use waste by-products for ruminant nutrition is increasing. Therefore, we replace the beet pulp and cereal straw from dry-non-pregnant goats' diet with orange leaves and rice straw with the objective of studying their effect upon intake, digestibility, energy efficiency, carbon and nitrogen balance, and methane emissions. Considering the huge quantities of crops by-products and pruning waste such as rice straw and citrus leaves produced annually worldwide, and their potential pollution capacity, recycling as feed for livestock is an alternative. The objective was to study these by-products effect on energy balance and methane emissions in 10 Murciano-Granadina goats at maintenance. The control diet (CTR) included barley straw and beet pulp while the experimental diet (ORG) consisted of rice straw and orange leaves. Differences were found for energy intake (248 kJ/kg of BW0.75 greater for CTR than ORG). The intake of metabolizable energy was 199 kJ/kg of BW0.75 lower in ORG than CTR, and the energy efficiency was higher with CTR (0.61) than ORG (0.48). Protein retained in the body was 9 g/goat greater with CTR than ORG, and fat retention in the body was approximately 108 g/goat greater with CTR than ORG. Despite more unfavorable energy balance in response to feeding ORG than CTR, the retention of body energy was always positive. Reductions in CH4 emissions were detected when goats were fed ORG diet (from 22.3 to 20.0 g/d). Overall results suggested that feeding orange leaves and rice straw was effective in reducing CH4 emissions without adversely affecting energy balance.This study was supported by LIFE Project, Spain (ref. LIFE2016/CCM/ES/000088 LOW CARBON FEED).Romero Rueda, T.; Palomares Carrasco, JL.; Moya, V.; Loor, JJ.; Fernández Martínez, CJ. (2021). Alterations in Energy Partitioning and Methane Emissions in Murciano-Granadina Goats Fed Orange Leaves and Rice Straw as a Replacement for Beet Pulp and Barley Straw. Animals. 11(1):1-14. https://doi.org/10.3390/ani11010038S11411

Inclusion of lemon leaves and rice straw into compound feed and its effect on nutrient balance, milk yield, and methane emissions in dairy goats

This study was supported by LIFE Project, Valencia, Spain (ref. LIFE2016/CCM/ES/000088 LOW CARBON FEED). The authors have not stated any conflicts of interestRomero Rueda, T.; Pérez Baena, I.; Larsen, T.; Gomis-Tena Dolz, J.; Loor, JJ.; Fernández Martínez, CJ. (2020). Inclusion of lemon leaves and rice straw into compound feed and its effect on nutrient balance, milk yield, and methane emissions in dairy goats. Journal of Dairy Science. 103(7):6178-6189. https://doi.org/10.3168/jds.2020-18168S61786189103

Treatment with tocilizumab or corticosteroids for COVID-19 patients with hyperinflammatory state: a multicentre cohort study (SAM-COVID-19)

Objectives: The objective of this study was to estimate the association between tocilizumab or corticosteroids and the risk of intubation or death in patients with coronavirus disease 19 (COVID-19) with a hyperinflammatory state according to clinical and laboratory parameters. Methods: A cohort study was performed in 60 Spanish hospitals including 778 patients with COVID-19 and clinical and laboratory data indicative of a hyperinflammatory state. Treatment was mainly with tocilizumab, an intermediate-high dose of corticosteroids (IHDC), a pulse dose of corticosteroids (PDC), combination therapy, or no treatment. Primary outcome was intubation or death; follow-up was 21 days. Propensity score-adjusted estimations using Cox regression (logistic regression if needed) were calculated. Propensity scores were used as confounders, matching variables and for the inverse probability of treatment weights (IPTWs). Results: In all, 88, 117, 78 and 151 patients treated with tocilizumab, IHDC, PDC, and combination therapy, respectively, were compared with 344 untreated patients. The primary endpoint occurred in 10 (11.4%), 27 (23.1%), 12 (15.4%), 40 (25.6%) and 69 (21.1%), respectively. The IPTW-based hazard ratios (odds ratio for combination therapy) for the primary endpoint were 0.32 (95%CI 0.22-0.47; p < 0.001) for tocilizumab, 0.82 (0.71-1.30; p 0.82) for IHDC, 0.61 (0.43-0.86; p 0.006) for PDC, and 1.17 (0.86-1.58; p 0.30) for combination therapy. Other applications of the propensity score provided similar results, but were not significant for PDC. Tocilizumab was also associated with lower hazard of death alone in IPTW analysis (0.07; 0.02-0.17; p < 0.001). Conclusions: Tocilizumab might be useful in COVID-19 patients with a hyperinflammatory state and should be prioritized for randomized trials in this situatio

Efecto de la presencia de "Penicilina G" en la leche de cabra sobre la elaboración y características del queso de tronchón curado

[ES] La presencia de residuos de antibióticos en los productos lácteos puede ser un problema para la salud pública, ya que ocasionan alergias, trastornos digestivos y desarrollo de resistencias, y también para la industria láctea por ser la causa de fallos tecnológicos y de calidad del producto final, en especial en los productos fermentados como es el caso del queso. Entre los antibióticos de mayor uso para el ganado lechero, se encuentra la penicilina G (bencilpenicilina) del grupo de los betalactámicos, debido a su elevada efectividad en el tratamiento de enfermedades infecciosas, escasa toxicidad y amplio espectro antibacteriano. La información sobre el efecto de la presencia de penicilina G en la leche sobre el proceso de elaboración y las características del queso es muy limitada. Por ello, el objetivo de este estudio ha sido analizar el efecto de la presencia de penicilina G en la leche de cabra sobre la fabricación y las características del queso curado. Para ello se han realizado elaboraciones de queso, por duplicado, a partir de leche cruda de cabra sin antibiótico y con adición de penicilina G a una concentración de 4 μg/kg equivalente al Límite Máximo de Residuos (LMR). Se han estudiado las posibles modificaciones en las características del queso (pH, composición, proteólisis, lipólisis, textura y color), así como la presencia del antibiótico, a distintos tiempos de maduración (1, 30 y 60 días). Además se ha evaluado la aceptación sensorial de las muestras a tiempo final de maduración. En base a los resultados obtenidos, se observa que la presencia de penicilina G solamente ocasionó diferencias en algunos parámetros de color, para la coordenada a* disminuyó y por lo contrario aumentó para el tono (h) en quesos con antibióticos. El tiempo de maduración afectó a todos los parámetros estudiados, encontrando a los 60 días valores mayores para la composición química, proteólisis, lipólisis, dureza, adhesividad, b*, croma y tono y menores para el pH, elasticidad, cohesividad, masticabilidad, luminosidad y a*. El análisis sensorial mostró que no se apreciaban diferencias significativas entre los quesos elaborados a partir de leche de cabra con y sin penicilina G, en relación a los atributos estudiados (apariencia, textura visual, olor, color y aceptación global). El contenido de antibiótico presente en el queso recién elaborado (día 1) fue de 4,8 μg/kg, no pudiendo ser detectado a los 30 y 60 días de maduración.[EN] The presence of antibiotic residues in dairy products can be a problem for public health because they cause allergies, digestive disorders and development of resistance, and also for the dairy industry as the cause of technical problems and product quality especially in fermented products it is as for cheese. Among the most commonly antibiotics used for dairy livestock, there is the penicillin G (benzylpenicillin), being to the beta-lactam group, due to its high effectiveness in the treatment of infectious diseases, low toxicity and broad antibacterial spectrum. Information on the effect of the presence of penicillin G in milk on the process of preparation and the characteristics of the cheese is very limited. Therefore, the objective of this study was to analyze the effect of the presence of penicillin G in goat’s milk on the manufacture and the characteristics of cured cheese. To this end elaborations of cheese were made, in duplicate, from raw goat milk without antibiotics and with addition of penicillin G to a concentration of 4 µg/kg equivalent to the Maximum Residue Limit (MRL). We have studied possible changes in the characteristics of the cheese (pH, composition, proteolysis, lipolysis, texture and color), and the presence of the antibiotic, ripening at different times (1, 30 and 60 days). It has also evaluated the sensory acceptance of cheeses at the end of the ripening period. Based on the results obtained, it is observed that the presence of penicillin G only caused some differences in color parameters, for the coordinate b* decreased and increased to the tone (h). The ripening affected all parameters studied, higher values for the chemical composition, proteolysis, lipolysis, hardness, adhesiveness, b*, chroma and tone and lower for pH, elasticity, cohesiveness, chewiness, luminosity are observed for cheeses of 60 days of ripening. Sensory analysis showed no significant differences between cheeses made from goat's milk with and without penicillin G, in relation to the attributes studied (appearance, visual texture, smell, color and overall acceptance). The content of antibiotic present in the fresh cheese (day 1) was 4.8 µg/kg, whereas it cannot be detected at 30 and 60 days of ripening.Romero Rueda, T. (2016). Efecto de la presencia de "Penicilina G" en la leche de cabra sobre la elaboración y características del queso de tronchón curado. http://hdl.handle.net/10251/72344.TFG