A scraped surface heat exchanger co

A scraped surface heat exchanger consists of a steel
shaft rotating in a stainless steel tube. A suitable coolant
(e.g. ammonia) cools the tube externally. The rotating
shaft is fitted with scraper blades. At high rotation
speeds, these blades scrape the inner surface of the tube
due to the applied centrifugal force. High internal pressure and shearing actions induce fast nucleation and
crystallization in a very short residence time. The length
of required crystallization time varies depending on the
fat compositions used in the formulations. Incorporation of a higher meltingbeta-primetending oil to a base
stock can induce the crystallization of the entire fat into
a stablebeta-primeform (Thomas III, 1978). The effects
of such formulation practice and processing conditions
have been studied extensively by Rivorola and co-workers (Rivarola et al., 1987) for blends of hydrogenated
sunflower and cottonseed oil. For strong beta-tending
sunflower oil, it was found that the tendency to crystallize in the beta-primeform increased with the increasing
cooling rate.Woodrow and deMan (1968b)investigated
the polymorphic behavior of milk fat after slow cooling
and rapid cooling. Slow cooling resulted in a mixture of
beta-primeandbetacrystals. Rapid cooling of milk fat
resulted in the formation of thealphaform which eventually transformed intobeta-primeandbetaupon holding the sample at 5

C. It has been known from the
literature that TAGs with simple and symmetrical fatty
acids tend to exhibit typically alpha, beta-prime, and
beta forms; whereas those with asymmetrical mixed
fatty acid moieties tend to form beta-prime crystals
(Hagemann, 1989; Sato, 2001). During processing, the
cooling rate and agitation is controlled. Hoerr (1960)
reported that rapid crystallization of a fat system induces the formation of small crystals throughout the solidifying mass. The small crystals then transform into
large aggregates. Narine and Marangoni (Narine &
Fig. 12. Production of shortening.
1040 B.S. Ghotra et al. / Food Research International 35 (2002) 1015–1048
Marangoni, 2002b)also observed these effects. This
property contributes to the creaming abilities of a
shortening (Hoerr, 1960), when small beta-primecrystals are preferred due to the increased ability to incorporate air bubbles.
10.3. Tempering and effects of emulsifiers
Tempering is the process whereby fats attain the physical state in which they are normally utilized. Tempering involves a time–temperature relationship where a
shortening is held for 1–10 days after initiation of
crystallization during processing at temperature which
may either be lower or higher than the temperature at
which the shortening is packed (Moziar et al., 1989).
During tempering, the crystals transform to the preferred polymorphic form. Lack of tempering adversely
affects the functional properties of shortening/margarine products. Tempering of shortenings result in significantly better functional properties. For example,
higher cake volumes can be obtained by using tempered cake shortening in a cake mix, whereas fresh,
untempered shortening gave lower cake volumes (Gillies, 1974). It has also been reported that tempering
affects the firmness of the shortening (Nor Aini, 2001).
Some shortening may continue to change in structure
even after the tempering process. This can lead to
among, other detriments, a potential defect in margarine texture called ‘graininess’ (Vaisey-Genser, Vane et
al., 1988). Proper temperature control during subsequent storage of the product reduces such undesirable
physical defects (Hoerr, 1960).
Tempering also delays the polymorphic transition
frombeta-primetobetacrystal forms (Moziar, de Man,
& de Man, 1989). Thebeta-form has a tendency to grow
in size upon standing; especially at room temperature.
When this happens there is a loss in creaming ability of
the shortening (Chrysam, 1985). Tempering of shortening and plastic fats at constant temperatures is an
expensive process. Maintaining and rotating inventories
of the products in large godowns creates logistic
problems.
Emulsifiers in shortening systems may be defined as
substances which have the potential to control polymorphism and modify the crystallization properties of
fats (Krog, 1977). The effect of emulsifiers on the crystallization and the development of polymorphic forms
of fat have been studied by a number of researchers
(Nakamura, 1997; Nasir, 2001; Rivarola, Anon, & Calvelo, 1988; Sato, 1999; Yuki, Matsuda, & Nishuimura,
1990). In addition to the aforementioned functions,
emulsifiers also primarily impart stability to emulsions,
control agglomeration of fat globules, and stabilize aerated systems (Krog, 1977). Nasir (2001)reported that
using de-oiled lecithin as an emulsifier delays the crystallization process and inhibits fat bloom in chocolate as
well as in other related food products. Yuki and coworkers (Yuki et al., 1990) observed an increase in the
rate of fat crystallization when sucrose fatty acid esters
(Palmitate and stearate types) are used as emulsifiers.
The addition of sorbitan esters stabilizes the intermediatebeta-primeform during crystallization and prevents the formation of thebeta-form (Garti et al., 1981,
1982). Sorbitan tristearate is effective as a crystal inhibitor in margarines. It is assumed that thebeta-prime
crystal form of fat crystal networks accommodate sorbitan tristearate. The stearic hindrances prevent the
formation of the more densely packedbeta-crystal form
(Krog, 1977). Canola oil in combination with an emulsifier hydrate containing monoglycerides, polysorbate
60, and sodium stearoyl lactylate, was used in a whitelayer cake formulation (Vaisey-Genser et al., 1987). It
was observed that such an emulsifier system permits a
reduction in the fat content of cake formulation from
53% to approximately 11% without loss in the quality.
Therefore, the use of emulsifiers has the potential to be
very economical for the oil and fat industry. However,
no comprehensive theory exists which links emulsifier
structure to function in the crystallization process.
10.4. Interesterification
Interesterification (IE) is an acyl rearrangement
reaction used to modify triglyceride melting and crystallization properties while maintaining their nutritional quality (although some nutritional quality may
be lost by the removal of beneficial fatty acids from the
sn-2 position of a TAG molecule). Interesterification
causes a rearrangement of fatty acids within, and
between TAGs on a glycerol backbone (Macrae, 1983).
This results in the formation of a new TAG that may
not have existed in the original fat. IE reactions can be
driven chemically or enzymatically. In chemical IE a
chemical catalyst such as sodium metal or sodium alkoxide is used to promote acyl rearrangement around
the glyceride molecule (Macrae, 1983). In enzymatic
IE, biocatalysts, such as microbial lipases are used for
the acyl migration around the glyceride molecule. The
acyl exchange can proceed in a controlled manner by
replacing the chemical catalysts with biocatalysts
(Macrae, 1983; Seriburi & Akoh, 1998). Lipase-catalyzed reactions, unlike chemical IE, do not produce byproducts (Seriburi & Akoh, 1998).
Two forms of reactions are recognized; random and
directed interesterification (Young, 1980). In directed
interesterification, the reaction mixture is cooled, which
causes the crystallization of high melting TAGs present
in the liquid oil phase. Such conditions disturb the
equilibrium of the liquid phase; thereby directing the
reaction to form more high melting fractions (Young,
1980). Cottonseed oil containing twenty four percent
saturated fatty acids is liquid at room temperature

Hasil (Bahasa Indonesia) 1:

Penukar panas permukaan scraped terdiri dari bajaporos berputar dalam tabung stainless steel. Pendingin cocok(misalnya amonia) mendingin tabung eksternal. Berputarporos dilengkapi dengan pisau pengikis. Di putaran tinggikecepatan, pisau mengikis permukaan bagian dalam tabungakibat gaya sentrifugal yang diterapkan. Tekanan internal yang tinggi dan geser tindakan menginduksi pembentukan inti cepat dankristalisasi dalam waktu sangat singkat tinggal. Panjangkristalisasi diperlukan waktu bervariasi tergantung padaKomposisi lemak yang digunakan dalam formulasi. Penggabungan dari meltingbeta-primetending minyak yang lebih tinggi ke basissaham dapat menginduksi kristalisasi lemak seluruh kestablebeta-primeform (Thomas III, 1978). Efekkondisi praktek dan proses perumusan seperti itutelah dipelajari secara ekstensif oleh Rivorola dan rekan kerja (Rivarola et al., 1987) untuk campuran terhidrogenasibunga matahari dan minyak biji kapas. Untuk kuat cenderung betaminyak bunga matahari, itu adalah menemukan bahwa kecenderungan untuk mengkristal di beta-primeform meningkat dengan semakin meningkatnyalaju pendinginan. Woodrow dan deMan diselidiki (1968b)perilaku polimorfik lemak susu setelah lambat pendinginandan pendinginan cepat. Lambat pendinginan mengakibatkan campuranBeta-primeandbetacrystals. Pendinginan yang cepat dari lemak susumengakibatkan pembentukan thealphaform yang akhirnya berubah memegang sampel di 5 intobeta-primeandbetauponC. It telah diketahui sejakliterature that TAGs with simple and symmetrical fattyacids tend to exhibit typically alpha, beta-prime, andbeta forms; whereas those with asymmetrical mixedfatty acid moieties tend to form beta-prime crystals(Hagemann, 1989; Sato, 2001). During processing, thecooling rate and agitation is controlled. Hoerr (1960)reported that rapid crystallization of a fat system induces the formation of small crystals throughout the solidifying mass. The small crystals then transform intolarge aggregates. Narine and Marangoni (Narine &Fig. 12. Production of shortening.1040 B.S. Ghotra et al. / Food Research International 35 (2002) 1015–1048Marangoni, 2002b)also observed these effects. Thisproperty contributes to the creaming abilities of ashortening (Hoerr, 1960), when small beta-primecrystals are preferred due to the increased ability to incorporate air bubbles.10.3. Tempering and effects of emulsifiersTempering is the process whereby fats attain the physical state in which they are normally utilized. Tempering involves a time–temperature relationship where ashortening is held for 1–10 days after initiation ofcrystallization during processing at temperature whichmay either be lower or higher than the temperature atwhich the shortening is packed (Moziar et al., 1989).During tempering, the crystals transform to the preferred polymorphic form. Lack of tempering adverselyaffects the functional properties of shortening/margarine products. Tempering of shortenings result in significantly better functional properties. For example,higher cake volumes can be obtained by using tempered cake shortening in a cake mix, whereas fresh,untempered shortening gave lower cake volumes (Gillies, 1974). It has also been reported that temperingaffects the firmness of the shortening (Nor Aini, 2001).Some shortening may continue to change in structureeven after the tempering process. This can lead toamong, other detriments, a potential defect in margarine texture called ‘graininess’ (Vaisey-Genser, Vane etal., 1988). Proper temperature control during subsequent storage of the product reduces such undesirablephysical defects (Hoerr, 1960).Tempering also delays the polymorphic transitionfrombeta-primetobetacrystal forms (Moziar, de Man,& de Man, 1989). Thebeta-form has a tendency to growin size upon standing; especially at room temperature.When this happens there is a loss in creaming ability ofthe shortening (Chrysam, 1985). Tempering of shortening and plastic fats at constant temperatures is anexpensive process. Maintaining and rotating inventoriesof the products in large godowns creates logisticproblems.Emulsifiers in shortening systems may be defined assubstances which have the potential to control polymorphism and modify the crystallization properties offats (Krog, 1977). The effect of emulsifiers on the crystallization and the development of polymorphic formsof fat have been studied by a number of researchers(Nakamura, 1997; Nasir, 2001; Rivarola, Anon, & Calvelo, 1988; Sato, 1999; Yuki, Matsuda, & Nishuimura,1990). In addition to the aforementioned functions,emulsifiers also primarily impart stability to emulsions,control agglomeration of fat globules, and stabilize aerated systems (Krog, 1977). Nasir (2001)reported thatusing de-oiled lecithin as an emulsifier delays the crystallization process and inhibits fat bloom in chocolate aswell as in other related food products. Yuki and coworkers (Yuki et al., 1990) observed an increase in therate of fat crystallization when sucrose fatty acid esters(Palmitate and stearate types) are used as emulsifiers.The addition of sorbitan esters stabilizes the intermediatebeta-primeform during crystallization and prevents the formation of thebeta-form (Garti et al., 1981,1982). Sorbitan tristearate is effective as a crystal inhibitor in margarines. It is assumed that thebeta-primecrystal form of fat crystal networks accommodate sorbitan tristearate. The stearic hindrances prevent theformation of the more densely packedbeta-crystal form(Krog, 1977). Canola oil in combination with an emulsifier hydrate containing monoglycerides, polysorbate60, and sodium stearoyl lactylate, was used in a whitelayer cake formulation (Vaisey-Genser et al., 1987). Itwas observed that such an emulsifier system permits areduction in the fat content of cake formulation from53% to approximately 11% without loss in the quality.Therefore, the use of emulsifiers has the potential to bevery economical for the oil and fat industry. However,no comprehensive theory exists which links emulsifierstructure to function in the crystallization process.10.4. InteresterificationInteresterification (IE) is an acyl rearrangementreaction used to modify triglyceride melting and crystallization properties while maintaining their nutritional quality (although some nutritional quality maybe lost by the removal of beneficial fatty acids from thesn-2 position of a TAG molecule). Interesterificationcauses a rearrangement of fatty acids within, andbetween TAGs on a glycerol backbone (Macrae, 1983).This results in the formation of a new TAG that maynot have existed in the original fat. IE reactions can bedriven chemically or enzymatically. In chemical IE achemical catalyst such as sodium metal or sodium alkoxide is used to promote acyl rearrangement aroundthe glyceride molecule (Macrae, 1983). In enzymaticIE, biocatalysts, such as microbial lipases are used forthe acyl migration around the glyceride molecule. Theacyl exchange can proceed in a controlled manner byreplacing the chemical catalysts with biocatalysts(Macrae, 1983; Seriburi & Akoh, 1998). Lipase-catalyzed reactions, unlike chemical IE, do not produce byproducts (Seriburi & Akoh, 1998).Two forms of reactions are recognized; random and
directed interesterification (Young, 1980). In directed
interesterification, the reaction mixture is cooled, which
causes the crystallization of high melting TAGs present
in the liquid oil phase. Such conditions disturb the
equilibrium of the liquid phase; thereby directing the
reaction to form more high melting fractions (Young,
1980). Cottonseed oil containing twenty four percent
saturated fatty acids is liquid at room temperature