Food Engineering / Gıda Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/12
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Article Citation - WoS: 69Citation - Scopus: 88Shelf Life Extension of Strawberry Juice by Equivalent Ultrasound, High Pressure, and Pulsed Electric Fields Processes(Elsevier, 2021) Yıldız, Semanur; Pokhrel, Prashant Raj; Ünlütürk, Sevcan; Barbosa-Canovas, Gustavo V.Nonthermal processing technologies have focused on the production of safe, fresh-like and high quality food products very much in line with current consumer demands. It is a high priority to maintain the quality attributes of the food during its shelf life. In this study; microbial stability, physicochemical properties and phytochemical characteristics of strawberry juice (SJ) pasteurized by ultrasonication (US) (55 degrees C, 0.29 W/mL acoustic energy density, 120 mu m amplitude, 3 min), high pressure processing (HPP) (300 MPa, 1 min), and pulsed electric fields (PEF) (35 kV/cm, 27 mu s) were evaluated during 42 days of storage at 4.C in comparison with conventional thermal pasteurization as a reference treatment (72 degrees C, 15 s). The nonthermal processes were equivalent in terms of E. coli inactivation since the selected processing conditions previously led to almost identical inactivation level (at least 5-log) of inoculated E. coli. Thus, the current study demonstrates how these equivalent US, HPP, and PEF treatments differ from each other in terms of their effect on SJ natural microbiota and quality characteristics during refrigerated storage. Results showed that US, HPP, and heat treatment ensured the microbial stability of SJ for at least 42 days while PEF extended the shelf life of SJ by at least 28 days based on the natural microbiota. No significant difference was found for the total soluble solids of the processed samples (p > 0.05) whereas acidity and pH of the samples varied during the storage period (p < 0.05). Immediately after processing, the total phenolic contents and antioxidant activities of SJ were better retained by HPP and PEF compared to thermal pasteurization. Furthermore, HPP and PEF significantly increased total anthocyanin content of SJ by 15 and 17% with respect to untreated SJ (p < 0.05). Phytochemical characteristics of processed SJ started to decrease after 7 days of storage irrespective of treatment type. HPP treated juices showed significantly higher levels of total anthocyanin and antioxidant activity at the final day of storage. Principal component and cluster analysis showed that the processed SJ samples had higher similarity to the untreated fresh SJ during storage up to 14 days, while the samples beyond this storage period clustered together and discriminated from the rest indicating a decreased similarity to the fresh juice. This study rendered simultaneous evaluation of several quality characteristics during storage of pasteurized strawberry juice based on the equivalent processing approach and multivariate data analysis. Under the selected processing conditions, HPP was the best option to extend the shelf life of SJ and enhance its phytochemical characteristics.Article Citation - WoS: 41Citation - Scopus: 43Changes in Quality Characteristics of Strawberry Juice After Equivalent High Pressure, Ultrasound, and Pulsed Electric Fields Processes(Springer Verlag, 2020) Yıldız, Semanur; Pokhrel, Prashant Raj; Ünlütürk, Sevcan; Barbosa-Canovas, Gustavo V.Understanding the efficacy of viable emerging technologies in preserving overall quality attributes and antioxidant characteristics of fruit juices is of great interest. This study aimed to evaluate the effect of high pressure (HP), ultrasound (US), and pulsed electric fields (PEF) processes on natural microbiota inactivation, as well as changes in physicochemical attributes and phytochemical content of strawberry juice (SJ). HP at 300 MPa (1 min), US at 55 degrees C (3 min) and 517.1 mW/mL acoustic energy density, and PEF at 35 kV/cm (27 mu s) using monopolar square pulses with 2 mu s pulse width were applied, and then compared with a conventional thermal pasteurization treatment (72 degrees C, 15 s). The nonthermal processes were equivalent in terms ofEscherichia coli(E. coli) inactivation since the selected processing conditions led to almost identical inactivation level (at least 5-log) of inoculatedE. coli. The current study analyzes why these equivalent processes had different effect on SJ quality. All treatments significantly reduced the initial natural microbiota (i.e., total mesophilic aerobic bacteria and yeast-molds) below 2 log CFU/mL. No significant changes were observed on the total soluble solid content (7.83-8.00 degrees Brix), titratable acidity (0.79-0.84 g/100 mL), and pH (3.45-3.50; except in sonication) between SJ processed samples and the untreated ones (p > 0.05). HPP and PEF significantly promoted higher retention of total phenolic content (TPC) and radical scavenging activity (RSA) than thermal pasteurization, and significantly enhanced total anthocyanin content (TAC) compared with unprocessed SJ. HPP and PEF increased the TPC (4-5%), RSA (18-19%), and TAC (15-17%) in comparison with unprocessed SJ. Multivariate data analysis tools, i.e., principal component analysis (PCA) and hierarchical cluster analysis (HCA), were successfully applied for discrimination and classification of SJ samples based on the similarities or differences among physicochemical and phytochemical characteristics. PCA and HCA indicated that HPP- and PEF-treated samples had similar enhanced properties in terms of phytochemical content and were superior to sonicated, thermally pasteurized, and unprocessed samples. The multivariate data analysis methods were very useful to compare and classify SJ quality characteristics as a function of the processing technology. This study demonstrated that the application of the equivalent processing approach may reveal new opportunities to produce equivalent or even enhanced quality fruit juices.Article Citation - WoS: 52Citation - Scopus: 69Identification of Equivalent Processing Conditions for Pasteurization of Strawberry Juice by High Pressure, Ultrasound, and Pulsed Electric Fields Processing(Elsevier, 2019) Yıldız, Semanur; Pokhrel, Prashant Raj; Ünlütürk, Sevcan; Barbosa-Canovas, Gustavo, VThe objective of this study was to evaluate the effectiveness of high pressure processing (HPP), ultrasound (US) and pulsed electric fields (PEF) for the pasteurization of strawberry juice (SJ). Acid-adapted Escherichia coli was used to inoculate SJ prior to treatment with HPP, US, and PEF. HPP was applied at several pressures (200-400 MPa) up to 2 min while US (120 mu m, 24 kHz) was conducted at 25, 40, and 55 degrees C up to 10 min in continuous pulsing mode. In order to avoid excessive use of SJ, PEF was performed using a model solution (MS) basically composed of citric acid (8 g/L), fructose (35 g/L), glucose (35 g/L), Na2HPO4 (0.2 M) and NaCl (5%) to simulate the SJ electrical conductivity, pH, and total soluble solid (TSS). A face-centered composite design was conducted for PEF processing at different electric field intensities (EFI) (25-35 kV/cm) and treatment times (5-27 mu s). Processing conditions were selected that resulted in 5-log CFU/mL inactivation of E. coli. HPP at 300 MPa for 1 min, and US at 55 degrees C (thermosonication) for 3 min reduced E. coli in SJ by 5.75 +/- 0.52 and 5.69 +/- 0.61 log CFU/mL, respectively. PEF treatment at 35 kV/cm, 27 mu s treatment time, 350 mL/min flow rate, and 2 mu s pulse width in monopolar mode resulted in 5.53 +/- 0.00 log reduction of E. coli in MS. Likewise, E. coli population in SJ was also reduced by 5.16 +/- 0.15 log after applying the same PEF conditions to SJ. No E. coli was detected in SJ subjected to conventional thermal pasteurization at 72 degrees C for 15 s. All technologies reduced the natural microbiota below 2 log CFU/mL in terms of the total aerobic bacteria and yeast-mold counts. Thus, this study identified the equivalent conditions for the SJ pasteurization by three nonthermal processing technologies. Industrial relevance: Consumers have an increasing interest towards fresh-like food products with desirable nutritional and sensorial attributes. High pressure, ultrasound and pulsed electric field are three relevant novel nonthermal technologies as alternatives to conventional thermal treatments. This study identified the processing conditions of these three nonthermal technologies for the pasteurization of strawberry juice based on equivalent inactivation of acid-adapted E. coli. From an industrial point of view, the established processing conditions are useful references for the development of novel berry juices. In addition to microbiological safety, this study on equivalent processing allows direct efficacy and quality comparisons of a given juice pasteurized by the three nonthermal technologies under consideration.