Chemistry Reference
In-Depth Information
of thick skin citrus fruits, such as grapefruits, is enhanced by the commercialization of
pre-peeling. This can be done by using mechanical peeling and chemical solubilization of
the membrane using sodium hydroxide (I N) at high temperature (90-95
◦
C). However, to
achieve high-quality products from citrus fruits with fragile and thick skin albedo, manual
methods are still commonly used. Alternatively, enzymatic treatments may be used to replace
or facilitate the process, thus drastically decreasing the manpower needed and achieving
gentler conditions. Citrus fruit skin is first scored or cut longitudinally. Albedo jellified
by fruit blanching, especially useful for thick albedos species and cultivars, is digested by
enzymatic treatment using Pectinolytic enzymes such as Peelzym (Novozymes) or Rapidase
C80 Max (DSM). This provides easy fruit peeling and removal of albedo parts that usually
stick on the surface of segments. This can be completed by residual albedo digestion which
facilitates segment separation and cleaning.
Segment membrane removal or segment extraction can be facilitated by hand or by chem-
ical and enzymatic dissolution. Manual extraction gives 'ready to can' cleaned segments;
chemical and enzymatic dissolution will break down the membrane which is removed after-
wards by water jet. This last step also removes chemicals or enzymes prior to canning and
sterilization. In this way no residual enzyme activity will be present which may hamper final
product quality.
Sterilization treatment and sometimes citric acid addition decreases the cohesion of vesi-
cles at this stage by partial dissolution of pectin and the calcium chelating pectates, thus pro-
viding visible depreciation of segments aspects. Enzymatic demethylation treatment using
NOVOSHAPE (Novozymes), Rapidase FP Super or Rapidase PEP (DSM), in combination
with calcium and demethylated pectin to form more stable and less soluble pectate acting as
adhesive in between the vesicles, preserves the texture and cohesion aspect of citrus segments
during sterilization and shelf life.
11.6
FRUIT FIRMING
Consumers want fruit in processed food to look and taste good (i.e. have a firm texture,
and a natural colour and flavour). However, most processed fruit, particularly soft fruit like
strawberries or raspberries, is damaged through mechanical and thermal treatment, freezing
or pasteurization. This has a negative effect on fruit texture, giving a mushy appearance and
consistency. Fruit texture is attributed to the structural integrity of the primary cell wall and
the middle lamella. Most ripe fruit has highly methylated pectin (HM pectin) above 50%.
Adding a pure pectinmethylesterase results in partial pectin demethylation. Pectic acid, so
formed, binds with bivalent cations like calcium, forming strong insoluble pectate gels in
situ (egg box conformation). The gelling characteristics of the pectin are altered from HM
pectin to low methylated pectin (LM pectin): LM pectins do not only form gels with sugar
and acid, but also with less soluble solids and calcium ions (unlike HM pectin). LM pectates
are also less soluble at high temperatures (often encountered during processing). The result
is increased firmness, allowing the fruit to maintain its shape and consistency throughout the
manufacturing process.
The DSM FirmFruit concept consists of combined fruit pectin demethylation in situ, with
fungal pectin methylesterase enzyme and creation of a strong pectate network with added
calcium, which overcomes the negative effects of mechanical and thermal treatment during
fruit processing.
