Two studies (storage and challenge tests) investigated the microbial shelf life combined with a semi-quantitative determination of volatile compounds of cloudy apple juices after power ultrasound (US) treatment. The sublethal injury of spoiler yeasts (Candida parapsilosis and Rhodotorula glutinis) was also evaluated. The maximum effect of sonication was observed 14 days post-treatment in both tests, especially on psychrotrophic count. Sublethal injury occurred only in C. parapsilosis. Microbiological data estimated the shelf life of sonicated juices to be around 21 days. The typical aroma compounds of the raw juices decreased quickly in control samples compared with sonicated ones. The flavor stability provided by US treatment seemed to be maintained for at least the first 14 days of cold storage. The US affected the shelf life of raw apple juices, probably due to yeast sublethal stress; some specific aroma compounds could be used as freshness or treatment markers.Keywords: sonication; apple juice; quality shelf life; volatile compounds; storage test; challenge test Se investigó el desarrollo microbiológico (respectivamente durante 28 y 60 días) a través de dos estudios (storage y challenge test) relacionando con la determinación semicuantitativa de los compuestos volátiles del jugo de manzana luego del tratamiento por ultrasonidos (US). Fueron evaluados los danos subletales de dos levaduras (Candida parapsilosis y Rhodotorula glutinis). En ambos casos fue observado el máximo efecto de la ultrasonificación después de 14 días del tratamiento, especialmente en la cuenta de bacterias sicrotróficas. Fueron observados danos estadísticamente significativos solo con C. parapsilosis. Los datos microbiológicos de los jugos tratados por ultrasonidos permitieron estimar como plazo de conservación en 21 días. La estabilidad del aroma después del tratamiento por ultrasonidos se mantiene constante por lo menos por los primeros 14 días de almacenamiento en frío. El tratamiento por ultrasonidos modifica la fecha de caducidad del jugo de manzana probablemente provocando estrés en las levaduras. Esta investigación también ha destacado que algunos compuestos específicos del aroma podrían ser utilizados como marcadores de frescura o del tratamiento mismo.

Fresh products, such as cloudy apple juice, could be preserved from early spoilage through the application of non-thermal processes such as sonication. However, shelf-life analyses based on microbiological and sensory evaluations are expensive and time consuming. Few studies have applied near infrared spectroscopy to evaluate the quality and decay of apple juices. Here, a feasibility trial was conducted to study the spectral behaviour at 1300-2500 nm combined with chemometric approaches. The shelf-life was monitored during two experiments, a challenge test with juices inoculated with spoilage yeasts (inoculated non-sonicated (INS)) and then submitted to sonication treatments (inoculated sonicated (IS)), and a storage test to evaluate the spoilage on non-inoculated juices (non-inoculated non-sonicated (NINS)) and sonicated noninoculated juices (non-inoculated sonicated (NIS)). These experiments were investigated at six different refrigeration times 7, 14, 21, 28 and 60 days. Two functions were modelled to describe the behaviours of the first principal component according to the storage time. In agreement with a previous chemical and sensory evaluation, this approach allowed us to highlight shelf-life end points of 7 and 14 days for non-sonicated and sonicated samples, respectively. Three different models were evaluated for classification purposes: (1) sonicated versus non-treated samples, (2) end-point shelf-life evaluation at seven days for the NINS and INS juices and (3) end-point shelf-life discrimination at 14 days for IS and NIS samples. A partial least square-discriminant analysis enabled a group classification with accuracy values ranging from 0.63 to 1.00. The application of a variable importance in projection index to interpret the wavelengths of the spectral features suggests a contribution of organic acids and lipids to the prediction of decay. A canonical discriminant analysis provided a clearer separation of samples according to the storage time, especially in relation to the two time thresholds of 7 and 14 days.

No abstract