Effects of ultrasound‐assisted blanching on the processing and quality parameters of freeze‐dried guava slices

Abstract

In this work, ultrasound‐assisted blanching (UAB) has been applied to study its effect on different physical and chemical characteristics and the total process time (TPT) of freeze‐dried guava slices (DGS). Additionally, the process energy consumption was estimated, and the overall process was modeled. UAB was applied at 5‐ and 10‐min exposure times and at 65°C to evaluate the polyphenol oxidase (PPO) and peroxidase (POD) activities. Then, guava slices were freeze‐dried and the TPT with and without UAB were compared. Also, the total polyphenol content (TPC), antioxidant activity (AA), and total color change (TCC) of the DGS were measured. TPT decreased significantly for both UAB exposure times. Moreover, at 65°C and 10 min UAB 36.0 ± 2.0% and 99.5 ± 1.0% reduction in PPO and POD, respectively, were observed. UAB samples resulted in lower TPC and AA. A significant reduction of the TCC was achieved with UAB. UAB decreased energy consumption during the process. Practical applications Freeze‐drying preserves the quality of a product to a greater extent than other drying techniques, such as convective drying. However, the use of freeze‐drying is limited by the high investment and operating costs. In this work, it is demonstrated that ultrasound‐assisted blanching (UAB) can markedly reduce the total lyophilization time during the processing of guava slices relative to that attained without this treatment (control). Additionally, due to the enzymatic inhibition achieved by UAB, the color of the dried material in storage was preserved to a greater extent than it was without this treatment. Although the use of ultrasound (US) entails additional equipment and personnel costs, the significant reduction in operational costs can allow the investment to be recovered.

Highlight on drying fruit slices with better retention of bioactive compounds

“…Chandra et al's (2021) pretreatment study confirms that a pretreatment prior to drying is essential for the retention of polyphenols. On the contrary, ultrasound‐assisted blanched and freeze‐dried guava slices showed 13.73 ± 1.75% and 28.47 ± 0.48% reduction in phenolics on 5‐ and 10‐min ultrasound treatment, respectively (Alvarez et al, 2019).…”

“…The antioxidants loss is attributed to several factors, such as drying time, thermal degradation, level of phenolic compounds, enzyme activity, and Maillard browning (Siow & Hui, 2013). Increased length of exposure of ultrasound for blanching before freeze‐drying guava slices boosts AA (Alvarez et al, 2019). Ultrasound‐aided osmotically dehydrated papaya slices demonstrated increased DPPH radical scavenging activity than untreated papaya slices, similar to the TPC trend.…”

Recent Trends in Pretreatment of Food before Freeze-Drying

“…Importantly, they observed that drying time was reduced by about 30% for blanched fruits. Another group of authors [26] studied the influence of ultrasound (US)-assisted blanching on the FD process in guava. They proved that such kind of pretreatments reduced, to a large extent, the peroxidase activity and, to a lower extent, the polyphenol oxidase activity.…”

“…The reduction in FD costs with high-quality products is still considered a challenge. However, adequate food pretreatment can significantly decrease the energy consumption associated with FD [25][26][27] and improve the quality of dried food [28,29]. FD allows obtaining products of very good quality, with a low final moisture content of 1-4% [5].…”

Analysis of ultrasound-assisted convective heating/cooling process: Development and application of a Nusselt equation

“…To improve processes, new methods and technologies have been proposed for enhancing heat exchange while reducing energy losses. Ultrasound (US) is a promising non-thermal food processing technology which has been recognized as an effective tool for intensifying heat transfer in different processes such as air drying, cooling, freezing, and blanching, increasing the efficiency of the processes while improving the quality of the final product [20] , [11] , [33] , [1] , [43] , [37] , [36] .…”