氏　　　名
 タン　ダニエル　レスリー　スウェード
TAN,Daniel Leslie,Suede
本籍（国籍）
 フィリピン
学位の種類
 博士（農学）
学位記番号
 甲　第１５１号
学位授与年月日
 平成１２年３月２４日
学位授与の要件
 学位規則第４条第１項該当
専　　攻
 生物資源科学専攻
学位論文題目
 Village Level Processing of Sweetpotato into Dried Chips, Flour and Grates
(小規模加工法によるサツマイモ製粉に関する研究)

論文の内容の要旨

　Sweetpotato is one of the most important crops in the Philippines. The roots are processed into dried chips, flour, dried grates and many other food items. Processing of these products are usually done in the villages, but the village level processing system has low efficiency and produces low quality products because of the kind of machines used and the weather-dependent drying process. Improving the system efficiency and increasing product quality is difficult because limited information is available about the village level processing system and products, that is needed in the design of efficient processing systems. This study aimed to provide additional information. 　This study specifically had the following objectives:

　1) to determine the performance of the village level processing machines, and the power requirement in milling the chips and the grates using the cross beater mill;

　2) to determine some physical characteristics of chips, flour and grates;

　3) to determine the thin-layer drying characteristics and compare the drying time of sweetpotato chips and pressed grates;

　4) to determine the chemical and thermal characteristics of the products of each processing operation in the village level production of chips, flour and grates; and

　5) to compare the differences of producing flour from chips and grates in terms of quality and the overall energy requirement per weight of flour produced.

　The results obtained from the studies were summarized as follows:

1. The PRCRTC Chipper/Grater had a pronounced power fluctuation during chipping, peaking during the loading of the roots, but higher fluctuation was observed in the grating operation. Kogane sengan had lower energy requirement in chipping and grating the roots than Shiro satsuma. The chipping capacity increased as the rpm of the blade was increased, together with the amount of crumbs present in the chips, but the average weight of the chips decreased. The amount of crumbs was significantly lower using the 45-degree as compared with the 90-degree blade-tip angle. For grating, at the same rpm range, the capacity increased but the fineness modulus of the grates decreased with an increase in blade rpm. Pressing the grates using the hydraulic presser at 5 kg loading rate reduced the moisture content of grates from more than 60% to about 50%, which was about the same when using the spinner.

　The attrition grinder had a more stable power fluctuation even in any kind and amount of material loaded to the hopper, but had the highest energy requirement among the machines evaluated. When grinding the chips at four different grinding conditions, almost the same average diameter of the first grind fine flour was obtained.

　The finisher consumed the least amount of net power among the village level machines. The first of the three identical compartments (immediately after the inlet hopper) gathered about 90% of the total fine flour. The same fine flour distribution was noted in the compartments between loading capacities and finisher rpm.

　With the existing village level root crop processing system, for Kogane sengan, the dried chips recovery at 12% moisture content (wet basis) is 33.3%, fine flour recovery of 21.4%, and the dried grates recovery of 30.4%.

　The power requirement in milling the different kinds of materials vary from each other, in which the small size Shiro satsuma chips recorded the highest and cassava grates the lowest.

2. Percent reductions of the sizes of fresh to dried chips were different between dimensions, with the thickness having the highest reduction (38.5% for Kogane sengan and 37.5% for Shiro satsuma), then followed by the width (21.2% and 26.5%) and then the length (7.0% and 20.2%). Bulk density of fresh sweetpotato chips was slightly higher for Kogane sengan than Shiro satsuma.

　The first ground fine flour of the chips was finer than the fine flour of the second ground material, while the coarse flour of the first ground chips was coarser than the second ground material. The grates had fineness modulus value in between the values of the first and second ground flour.

　The angles of repose of fine materials (first and second grind fine flour, and materials milled using the cross beater mill) were generally higher than the chips, grates and coarse flour for both varieties. Kogane sengan exhibited higher angle of repose than Shiro satsuma for the coarse flour, but lower for the fine materials. The angle of repose of most materials increased as the moisture content increased.

3. The drying rate of chips at 70°C in the two airflow rates composed of two falling rate periods, but not in the other drying conditions. No constant rate period was observed in all drying conditions. For pressed grates, only a decreasing falling rate period forming a curve line was observed. The drying air temperature and airflow rate had significant effects on the drying rate of chips and pressed grates, and their effects were decreasing as the moisture content of the samples decreased.

　The modified Page equation is the appropriate model of the thin-layer drying of sweetpotato chips and pressed grates. The modified Page equation with the generalized k and n values fit the data well.
At 70°C, and 0.145 m3/s/m2 airflow rate, the computed time to dry the sample to a 12% moisture content (w. b.) was 36 minutes for pressed grates and 166 minutes for chips.

4. For chips processing, the starch contents of the products at different processing stages were almost the same from the fresh roots. The trend was the same for both varieties, but Kogane sengan had higher starch content than Shiro satsuma. The sugar contents of the products for Kogane sengan had significant differences, but none for Shiro satsuma. The fiber contents of the second grind fine and coarse flour were higher than the other products, for Kogane sengan. However, the trend was not the same for Shiro satsuma. Highest ash contents were observed in the second grind coarse flour, while highest fiber contents were noted in the second grind fine flour for the two varieties.

　Highest enthalpy values were noted in the first grind fine flour, and the lowest values were noted in the second grind coarse flour, for the two varieties, but Kogane sengan had generally　higher enthalpy, and lower onset and peak temperatures than Shiro satsuma. For grates processing, the starch content of the pressed grates was the highest compared to the fresh roots and fresh grates of both varieties, with Kogane sengan exhibiting higher values than Shiro satsuma. A decreasing sugar content was noted from the fresh roots, to fresh grates, then to pressed grates for both varieties but higher values were noted for Shiro satsuma than Kogane sengan. The pressed grates had the lowest ash content and the highest fiber content among the products, for both varieties.

　The pressed grates of the two varieties had the highest enthalpy values among the products, with Kogane sengan exhibiting higher enthalpy values, and lower onset and peak temperatures than Shiro satsuma.

5. Applying the natural sun drying method in the village level processing system seldom produces good quality products due to changing weather conditions. Therefore, the application of artificial drying is very important in order to produce good quality products even though artificial drying consumes more energy than sun drying. Comparing the chips and grates processing systems in the production of flour by artificial drying, the processing of flour from grates was found out to be more advantageous in terms of energy requirement than that of processing the flour from chips.

和　文　要　旨

　サツマイモはフィリピンでは重要な農産物のひとつであり，乾燥チップ，乾燥粉および乾燥グレイツなどに加工されている。村落レベルで行われている小規模加工は，使用する機械の種類および乾燥工程が天候に左右されるなどの理由により，効率は低く品質も良くない。従って，加工システムの効率の改善と品質の向上のためには，効率的な加工システムの設計が必要とされる。

　本研究ではフィリピンで行われているサツマイモの村落レベルの加工プロセスおよび製品（乾燥チップ，乾燥粉および乾燥グレイツ）の品質を評価することを目的とし，日本におけるサツマイモの加工品種であるコガネセンガンとシロサツマを用いて実験を行った。はじめに，フィリピン根菜類研究・訓練センター（PRCRTC）が開発したチッパ・グレイタおよび選別機の性能を調べ，クロスビータミルによる乾燥チップやグレイツの製粉に要する電力を測定した。つぎに，チップ，乾燥粉およびグレイツの物理特性を調べた。さらに，チップとプレス後の脱水グレイツの薄層乾燥特性を解析した。また，製品の一般成分および示差走査熱量計（DSC）による熱特性を調べた。つぎに，乾燥チップおよびグレイツの製粉に要する電力量の比較，検討を行っている。 これらの研究成果は，次のように要約される。

1．PRCRTCチッパ・グレイタは，チッピング中に電力消費の著しい変動を，さらに原料投入時に最大電力消費量を示すが，グレイティングに要する電力の変動はチッピングよりも大きい。コガネセンガンはシロサツマよりチッピングやグレイティングに要するエネルギは低い。チッピング性能は刃の回転数が高くなるほど増加するが，チップの平均重量は減少した。チッピングと同じ回転数でグレイティングすると，能力は高くなるが，グレイツの粒度係数は刃の回転数が高くなるほど減少した。粉砕機はチッパ・グレイタや選別機よりもエネルギ消費量は高いが，消費電力は安定しており，原料の投入量に影響されない。選別機の正味電力量はチッパ・グレイタや粉砕機に比べ最も低い。選別機の原料投入口に最も近い１番口の回収率は，全粉末の約90％であった。コガネセンガンの場合，原料重に対する乾燥チップ，乾燥粉および乾燥グレイツの製品重量割合は12％水分換算で，それぞれ，33.3，21.4，30.4%であった。

２．シロサツマの生鮮チップを乾燥したところ，チップの大きさに関しその減少率は７％から38.5%となり，コガネセンガンよりも減少の程度は高かった。コガネセンガンの生鮮チップの容積重はシロサツマよりわずかに高い傾向を示した。チップの１回目の粉砕で得られた乾燥粉は２回目の粉砕のものより微細であった。グレイツの粒度係数は最初の粉砕による粒度係数と２回目の粉砕のそれとの中間の値となった。微粉（１回目と２回目の粉砕による微粉およびクロスビータミルを用いて粉砕したもの）の割合は両品種ともにチップ，グレイツ，粗粉よりも高かった。コガネセンガンの粗粉の安息角はシロサツマより大きいが，微粉の安息角は低かった。安息角は試料水分が高いほど大きくなった。

３. ２種類の風速でチップを乾燥したところ，すべての乾燥条件下で，恒率乾燥期間は認められなかった。第1，第2の減率乾燥期間は70℃ではみられたが，51，33℃の条件ではみられなかった。乾燥空気温度と風速はチップや脱水グレイツの乾燥速度に有意に影響したが，その効果は試料水分の減少とともに低下した。Pageの修正式はサツマイモのチップと脱水グレイツの薄層乾燥モデルとして妥当である。70℃，0.145m3/s/m2の条件で，試料を12％水分まで乾燥するのに要する時間を試算した結果，脱水グレイツでは36分，チップでは166分となった。

４. チップは生鮮時の成分に比べ，各製品のデンプン含量には変化が認められない。糖分については品種間にやや差異が認められる場合がある。繊維については2回目の粉砕製品にやや多い傾向が認められるが，品種により異なる。灰分についても明確な差異を認めない。グレイツの場合は生鮮時に比べ，明らかに搾汁後にデンプン含量の割合が増し，逆に糖分含量が減少する。 熱特性は，糊化熱，糊化開始温度及びピーク温度にチップ，グレイツ間に差異はほとんどない。品種間にやや差異を認めた。

５. 天日乾燥による村落レベルのサツマイモ加工システムは，天候に大きく支配されるのでチップからの加工法に限定され，かつ製品の品質も不安定となる。そこで人工乾燥を行うことにより，全エネルギ消費量は増加するものの，グレイツからの加工法はエネルギ消費量や品質面で有利となる。