ID: 2258

• Title:
  Effect of mild pasteurization assisted with PEF on goat milk for goat cheesemaking
  
  Authors:
  

  Araújo, Alberta - IPVC, CISAS, CEB
  Barbosa, Carla - IPVC, CISAS, LAQV-REQUIMTE
  Fernandes, Paulo - IPVC, CISAS
  Romão, Alexandre - IPVC
  Alves, M.R - IPVC, CISAS
  
  IPVC - Instituto Politécnico de Viana do Castelo
  CISAS – Centro de Investigação e Desenvolvimento em sistemas agroalimentares e sustentabilidade, IPVC, Viana do Castelo, Portugal;
  3 CEB – Centre of biological engineering, University of Minho, Braga, Portugal. 
  4 LAQV-REQUIMTE, Faculdade de Farmácia, Porto, Portugal

  
  
  Abstract:
  Background and objectives:
  
  Combining PEF (Pulsed Electric Field) with mild heating has been explored as an alternative treatment to enhance safety and preserve the quality of milk and its products. It is well known that high temperature treatments can promote physical and organoleptic alterations along with nutritional losses [1, 2].
  
  The objective of this study was to compare the effectiveness of two different treatments in goat milk processing and cheesemaking: a combination of PEF and mild heat treatment, and a traditional thermal treatment (HT) commonly employed in the dairy industry. For that, raw goat milk was pasteurized using PEF+HT at 63 °C for 6 s and just an HT at 75 °C for 3.4 s. A laboratory scale PEF unit (EPULSUS®-LPM1A-10 by EnergyPulse Systems, Lda, Portugal) was used, and tests were performed in continuous mode, using a fixed electric field strength of 10 kV/cm, 50 µs pulses width, 3 Hz and a flow rate of 2.92 Lh-1. Heat treatments were carried out in a Armfield FT74XTA HTST/UHT system. After milk pasteurization it was produced cheese in two independent batches for each studied treatment. Microbial, physicochemical, and organoleptic properties were evaluated during cheese ripening for 5, 15 and 25 days.
  
  
  
  Methods:
  
  Microorganism quantification and identification were carried out using established methods. Specifically, ISO 4833-1:2013 was used to count microorganisms at 30 °C on PCA (Scharlau). Enumeration of Enterobacteriaceae in VRBG (Scharlau) was performed according to ISO 21528-2:2017. For E. coli quantification in TBX (Biomerieux), ISO 16649-2:2001 was used. ISO 6579-1:2017 and ISO 11290-1:2017 were used for the detection of Salmonella spp. and L. monocytogenes, respectively.
  
  Milk physicochemical parameters were pH (AOAC 981.12:2016); total soluble solids (TSS) (AOAC 932.12:2016) and titratable acidity (TA) (AOAC 947.05:2016) and conductivity.
  
  Cheese physicochemical parameters were pH (AOAC 981.12-2016); moisture content (AOAC 948.12-2002); TA (AOAC 947.05-2016); water activity; texture parameters (texture profile analysis) and L, a and b colour parameters (CIE Lab). Sensory evaluation was performed by a 10 assessors panel according to Quantitative Descriptive Analysis (QDA) methodology, focusing on aroma and flavour attributes.
  
  
  
  Main results and conclusions:
  
  Concerning microbial stability, previous results revealed that PEF+HT treatment at 63 °C (6 s) caused the same reduction effect on the population of Listeria monocytogenes as compared to HT milk samples at 75 °C (3.4 s). No significant differences were observed in the total number of mesophilic microorganisms present between both types of cheese. E. coli and Enterobacteriaceae, were below of the detection limit in any of the studied cheese samples along with L. monocytogenes nor Salmonella spp. which were not detected after enrichment.
  
  
  
  Physicochemical evaluation revealed that no significant differences were detected among milk samples in both treatments with respect to pH, TA and TSS. Although, conductivity decreased as temperatures possibly due to decrease in Ca2+, one of the main constituents of the casein micelle’s.
  
  
  
  In relation to cheese physicochemical properties (pH, aw, moisture content and total acidity) no significant differences were observed. Exception made for colour parameters of cheese produced with PEF+HT milk being lighter (L higher values) and more yellow (higher b* values), also observed over ripening. Sensory scores for caprylic, goaty, acetic flavour increased over time, but between treatments only small differences were perceived in cheese with 5 days. Firmness and cohesiveness of PEF+HT samples was lower than HT samples even over storage time.
  
  
  
  In general concerning quality parameters, a similar behaviour was observed between treatments during ripening period. A microbial load reduction with a significantly lower temperature presents advantages in nutritional terms, particularly relevant in a product that presents stability problems, when subjected to higher temperature treatments due to its chemical composition.
  
  
  
  Acknowledgments:
  
  Authors acknowledge to Prados de Melgaço for kindly supplying the raw goat milk
  
  Keywords:
  goat milk, pasteurisation, goat cheese, quality
  
  Refs:
  1. Deshwal, G.K., S. Tiwari, and S. Kadyan, Applications of emerging processing technologies for quality and safety enhancement of non-bovine milk and milk products. LWT 2021, 149 111845. 2. Zhang, Z.-H., et al., Non-thermal technologies and its current and future application in the food industry: a review. International Journal of Food Science & Technology 2019, 54 (1): p. 1-13.
  
  Topic 1:
  10. Food safety and food preservation
  
  Topic 2:
  2. Biophysics and biochemistry of interaction mechanisms