Development and performance evaluation of grape debunching machine for production of raisins and stemless table grapes

Abstract

Chemical pretreatment before drying is a practice in raisin making which has many limitations and use of chemical shall be discouraged. A new process is being developed with physical pretreatment. The process requires intact grape berries for further processing. Therefore, a grape debunching machine has been developed for separation of intact berries from the bunch. The machine consists of central rotor with helical fingers. The rotor assembly is surrounded by perforated trough through which the detached berries drop. The performance of the machine was evaluated with “Thompson Seedless” table grape for debunching efficiency and damage to berries. The rotor speed (80–120 rpm) and concave clearance (5–25 mm) were selected as independent parameters. The debunching efficiency and percentage of damaged berry were in the range of 77.17–98.73% and 5.75–11.82%, respectively. The maximum debunching efficiency (94.33%) and minimum berry damage (7.10%) was obtained at rotor speed of 100 rpm and concave clearance of 15 mm. The capacity of grape debunching machine was found to be 145.2–150.2 kg/hr for different grape varieties, namely Thompson Seedless, Manik Chaman, and Fantasy Seedless. The developed machine will be useful in production of raisins without use of chemicals and stemless table grapes. Practical applications The conventional process of raisin making involves intensive use of chemicals right from dipping of harvested grape bunch in a solution of ethyl oleate (1.5%) and potassium carbonate (2.5%), intermittent sprays, and further use of booster and sulfur dioxide for color improvement. The intensive use of chemicals triggers the food safety issues. Furthermore, the process requires longer drying time, involves more number of unit operations, and fetches losses of grapes. To address these issues, an alternative chemical‐free process has been developed by the authors of this investigation for the production of raisins. This process requires the grape berries to be individualized before further processing which is tedious and time consuming if done manually. Therefore a grape de‐bunching machine has been developed for separation of intact grape berries which can be further processed into raisins at industrial scale without use of chemicals. The developed machines will find applications in the minimally processed/individual quick freezing (IQF) of table grapes for which there is an increasing market especially in super market.

Novel alternative pretreatment approaches for production of quality raisins from grapes: Opportunities and future prospects

“…Different chemicals have been tried for this purpose and presently alkali based chemicals namely, sodium hydroxide (NaOH) or potassium carbonate (K 2 CO 3 ) and oil emulsion (ethyl oleate) are being commercially used by the raisin producers (Ashtiani et al, 2020; Carranza‐Concha et al, 2012; Doymaz, 2006; Doymaz & Pala, 2002; Patidar et al, 2021; Wang et al, 2017). Recently, some alternatives to chemical pretreatment such as surface abrasion (Adiletta et al, 2016; Di Matteo et al, 2000; Pawar, Giri, & Sharma, 2021; Pawar, Giri, Sharma, & Kotwaliwale, 2021; Senadeera et al, 2014) thermal and nonthermal techniques (Dev et al, 2008; Khiari et al, 2019; Salengke & Sastry, 2005) are being explored by the researchers.…”

“…The whole abrasive pretreatment process for the grapes consists of a series of unit operations starting from the separation of berries from grape bunch called de‐bunching of grapes (Pawar, Giri, & Sharma, 2021). The process flow chart of all unit operations of abrasive pretreatment is shown in Figure 4.…”

“…Water stress to grape vines before harvest will help for easy separation of berries from the bunch. The authors (Pawar, Giri, & Sharma, 2021) have developed a grape de‐bunching machine that separates the intact berries from bunches of grapes with maximum de‐bunching efficiency of 94.33% and minimum berry damage of 7.10%. The de‐bunching mechanism consists of a central shaft/rotor in which the fingers were arranged in a helical manner.…”

“…Only the waxy cuticle layer from the outer surface of peels of the fruits gets removed with mild abrasion; hence there is no damage to the nutritive value of products in abrasive pretreatment. The study by the authors (Pawar, Giri, & Sharma, 2021) reported that abrasive pretreatment of grapes did not affect the nutritional and bioactive compounds of raisins except slightly higher browning index. Phenolic compounds like chlorogenic and coumaric acids were retained well in abrasive‐treated goji berry samples.…”

“…Though the color of raisins produced with the abrasive process is slightly dark, this method has the potential to produce safe and natural raisins without the use of any chemicals, and it can be adopted easily for industrial‐scale raisin production. The drying rate of abrasive pretreated grapes is significantly higher and it can reduce the total processing time of raisins as well (Adiletta et al, 2016; Pawar, Giri, & Sharma, 2021).…”