Washing, Peeling and Cutting of Fresh-Cut Fruits and Vegetables - Minimally Processed Foods - page 62

increases due to acceleration of physiological process and the exposure of the
tissues to microorganisms. The shelf-life and quality of fresh-cut produces could
be compromised with the peeling. The goals of optimum peeling operation are
(Radhakrishnaiah Setty et al. 1993 ):

1. Minimizing product losses,
2. Types of products e.g., potato products,
3. Minimizing heat ring formation e.g., apple, potato,
4. Minimizing energy and chemical usage, and
5. Minimizing the environmental pollution

Peeling operation can be grouped under following categories:

• Manual peeling (knife or blade),
• Mechanical peeling (abrasive devices, devices with drums, rollers, knifes or
blades and milling cutters),
• Chemical peeling,
• Enzymatic peeling, and
• Thermal peeling (Flame or dry heat peeling, steam or wet heat peeling, thermal
blast peeling, and vapour explosion or vacuum peeling)

4.3.1 Manual Peeling

Manual peeling is performed using stationary or rotatory hand peelers or knives
against the surface of fruits and vegetables. Fresh-cut fruit and vegetables with good
microbiological quality can be obtained by this method. Klaiber et al. ( 2005 ) reported
that knife peeling caused less wounding in comparison to abrasion peeling in carrots.
This can result lower microbial contamination after processing. On the other hand,
O'Beirne et al. ( 2014 ) did not fi nd differences between coarse abrasion and hand
peeled carrot surfaces considering E. coli O157:H7 cells attached to the surface after
peeling. However, despite of good results obtained by manual peeling, this method is
limited to small scale processing and is laborious and requires more time.

4.3.2 Mechanical Peeling

Mechanical peeling includes different types of process that interact directly with
skin and then removes the skin. Common commercial mechanical peelers are abra-
sive devices, drums, rollers, knives and milling cutters (Shirmohammadi et al.
2012 ). Mechanical peelers can provide high quality fresh fi nal products and they
are environmental friendly and nontoxic. The main factors affecting the peeling
process are mechanical and physical properties of fruit and vegetable tissues,
such as skin thickness, fi rmness, toughness, variety, rupture force, cutting force,
maximum shearing force, shear strength, tensile strength and rupture stress