Ꮫ ఩ ㄽ ᩥ ࡢ せ ᪨(Summary of Dissertation)  ㄽᩥ㢟┠   Effect of trehalose on the mechanical properties of deep-fried foods    (ࢺࣞࣁ࣮ࣟࢫࡀࣇࣛ࢖㣗ရࡢຊᏛⓗᛶ㉁࡟ཬࡰࡍᙳ㡪)                    ᗈᓥ኱Ꮫ኱Ꮫ㝔⤫ྜ⏕࿨⛉Ꮫ◊✲⛉                   Food and AgriLife Science ࣉࣟࢢ࣒ࣛ                   Ꮫ⏕␒ྕ D201930
                   Ặ  ྡ LE NGOC DANG TRINHDeep-frying is one of popular cooking methods to produce dry foods having desirable andcharacteristic flavor and texture. Deep-frying is achieved by immersing food stuff into theheated oil (approximately 150 ºC~200 ºC). In case of tempura, tempura is cooled down at room
temperature, and the fry coating becomes glassy state at least at the outer part. The glassy fry
coating shows a favorable brittle texture. When storage time is prolonged, the fry coatingchanges from brittle texture to ductile texture because glass to rubber transition (briefly, glasstransition) occurs through water sorption originating from the atmosphere moisture and/orfrom the food stuff. Temperature of which glass transition occurs is denoted as glass transition
temperature (Tg). Food product is glassy state at a lower temperature than the Tg, and the glassy
porous food shows brittle texture because of its high elasticity. The glassy food becomesrubbery state at a higher temperature than the Tg, and the rubbery food shows ductile texture
because of the reduced elasticity. Glass transition also occurs even at a constant temperaturewhen water content change, because the Tg of hydrophilic amorphous materials decreases with

an increase in the water content because of water plasticizing effect. Water content of which
the Tg becomes 25 ºC (typical room temperature) has been described as critical water content(wc). In addition, water activity (aw) of which the Tg becomes 25 ºC has been described as
critical water activity (awc). The higher wc and awc, the greater resistance to the physicaldeteriorations induced by water sorption. To maintain brittle texture of fry coating as long as
possible, it is important to elevate the wc and/or awc of fry coating.
Differential scanning calorimetry (DSC) is the most common technique to determine the Tgof amorphous materials. However, it is difficult to determine the Tg of starchy foods because
unclear glass transition behavior is observed in a broad temperature range. In this case,thermomechanical approach is more effective. In a previous study, it was demonstrated thatthe glass transition of fried batter particles (agedama) could be detected by thermal rheologicalanalysis. It is known that thermal Tg determined by DSC does not always agree with the Tg
determined by thermomechanical approaches. Thus, the Tg determined by thermomechanicalapproaches is distinguished as “mechanical Tg”.
It is known that the Tg of amorphous materials can be controlled by the compositions. For
example, Tg of amorphous polymers decreases with an increase in small molecules because of
their plasticizing effect. However, the plasticizing effect of small molecules on the mechanical
Tg of the fried batter particles does not always obey to the plasticizing behavior. In our previous
study, it was demonstrated that the mechanical Tg of fried batter particles could be elevated by
the addition of trehalose. As one of possibilities, it is suggested that trehalose filled the defects
in the amorphous amylopectin (the major component of the fried batter particles) and themechanical strength was enhanced. This suggestion is based on “anti-plasticizing effect”
explained in the previous studies.
To clarify physical modification effect of trehalose on the fried batter particles in more detail,this study aimed to understand effect of trehalose content on the mechanical properties of friedbatter particles. In addition, freeze-dried waxy starch (amylopectin) was employed as a modelof fried batter particles. The freeze-dried starch solid has numerous pores formed by ice
sublimation; the glassy porous solid is similar structure to fried batter particles. Amylopectin
is the major component of fried batter particles, and chemical reactions and thermal
degradation are highly diminished by freeze-drying. Thus, freeze-dried waxy starch wasexpected to be an effective model for the better understanding of the physical modificationinduced by trehalose addition.
Chapter 1 stated the background and purpose of this study.
Chapter 2 showed fundamental details regarding materials and experimental techniques usedin this study.
Chapter 3 reported effect of trehalose content on the oil content, water content, aw, mechanicalglass transition, and texture properties of fried batter particles. Wheat flour and chilled water
were mixed at the weight ratio of 1.0 : 1.6, and trehalose (0, 5, 10, 20%, against dry wheatflour) was added into there in an iced water bath. The batter was dropped into heated oil andfried at 180 ºC for 4 min. The 10% trehalose sample was the lowest oil content, water content,and aw. In addition, 10% trehalose sample was higher mechanical awc, lower first fracture force,and higher number of fracture peaks than 0% and 5% trehalose samples. There were similareffects on the mechanical awc and fracture properties between 10% and 20% trehalose samples.
This suggests that 10% trehalose is an optimum additive content for the brittle texture of deepfried foods. The results convey the molecular mechanism involved in the physical modificationof trehalose on fried batter particles.
Chapter 4 reported the effect of trehalose content on the texture properties and true density offreeze-dried waxy starch. Waxy starch was put into a vial, and distilled water was added. For

the preparation of the samples containing trehalose, 5%, 10%, 20%, and 40% trehalose (on dry
weight basis) was added. Starch in the mixture was gelatinized, and the gelatinized mixture
was freeze-dried. The first fracture force and the number of fracture peaks of freeze-driedporous solids were an almost equivalent behavior to those observed in fried batter particles. In
addition, it was demonstrated that freeze-dried powder containing 10% trehalose sample wassignificantly higher true density than the others. This result strongly supports the suggestion
based on the anti-plasticizing effect; trehalose fills the defects in the amorphous amylopectin
and the mechanical strength is enhanced.
Chapter 5 claimed the general discussion according to the results. When gelatinization ofwheat starch occurs in the presence of trehalose, the trehalose is partially incorporated into thegelatinized wheat starch because of the hydrophobic interaction induced by oil. Thus, thetrehalose molecules will act as “internal trehalose”. The trehalose except for internal trehalose,on the other hand, will locate at the interfacial parts of amylopectin. Since internal trehalose
can fill the gap spaces of amylopectin, oil uptake is reduced. In addition, evaporation of water
is promoted because water molecules are excluded from gelatinized wheat starch by internaltrehalose. The fact that freeze-dried amylopectin containing 10% trehalose was the highest true
density suggests that the gap space of amylopectin is almost saturated by 10% trehalose
addition. This corresponds to the lowest oil content, water content, and aw of 10% trehalose
sample. In addition, the fact that 10% trehalose sample was higher mechanical awc than 0%
and 5% trehalose samples is explained.
Since fractures intrinsically occur at the physically weak points in the structure, interfacial
trehalose plays a role of fracture points. Thus, the first fracture force decreased, and the numberof fracture peaks increased by the addition of trehalose.
Water is a much lower molecular size and much higher molecular mobility than trehalose.

Water molecules within the glassy polymer are mobile at ambient temperature. Thus, there will
be an unclear distinction between internal and interfacial water molecules in glassy
amylopectin. Water molecules will fill gap spaces in the internal and interfacial part ofamylopectin that trehalose cannot sufficiently fill, and thus fracture points attributed tointeractions between interfacial trehalose and amylopectin can be physically strengthened bywater. Consequently, the first fracture force increased linearly, and the number of fracture
peaks decreased linearly with increasing aw, even in the glassy state.
Chapter 6 gave the conclusion for this study and outlook for the future subject. This study
employed fried batter particles as a fry coating model. Fry coating coats wet food stuff, andthus diffusion of water molecules from the food stuff to the fry coating occurs quickly. Since
deep-fried foods are in non-steady state, there is a gradation of water content and temperaturebetween inner and outer parts. It is practically important to understand the kinetic propertiesof fry coating.