2. Methods2.1. MaterialsWheat flour with medium gluten strength was a gift fromChia-Fha Enterprise Co. Ltd. (Taichung, Taiwan). Theapproximate composition of wheat flour on a wet basis, asanalyzed by the AACC [20] methods, were 12.1% moisture,11.0% crude protein, 0.6% crude fat, and 0.4% ash contents.Commercial instant dried yeast and sodium stearoyl 2-lactylate were obtained from S. I. Lesaffre Co. (Marcq,France) and Danisco Ingredients (Penang, Malaysia), respectively.Food-grade sucrose and shortening were purchasedfrom Taiwan Sugar Co. (Tainan, Taiwan).The core of fresh pineapple (Ananas comosus L. Merr.) wasobtained as a byproduct from a local fruit processing factory.Pineapple core fiber was prepared in accordance with themethod proposed by Chien and Kang [16], with some modifications.In brief, pineapple cores were washed, cut (<1 cmthick), blanched (100C for 15 minutes), drained, air-dried(50C for 24 hours), and crushed. The crushed samples werethen extracted by 80% ethanol for 12 hours. The residues aftercentrifugation were air-dried (50C for 24 hours) and milled toa particle size of less than 0.42 mm. Three fractions of PCFwith different particle sizes were collected by sieving with 40mesh, 60 mesh, and 100 mesh. Total, insoluble, and solubleDFs of the PCF were analyzed by AOAC methods [21]. Functionalproperties (e.g., swelling power and water-holding capacity)were measured by the method of Huang et al [22], withsome modifications. The PCF (1 g) was hydrated with 20 mL ofdistilled water in a calibrated cylinder at room temperature.After equilibration (24 hours), the bed volume was recordedand the swelling power was expressed as milliliters of swollensample per gram of dry sample. Furthermore, PCF (1 g) wassoaked in 10 mL of distilled water for 24 hours and thencentrifuged at 1000g for 20 minutes. The supernatant wasdecanted into a graduated cylinder and the volume of excesswater was read. Hence, Water-holding capacity was expressedas milliliters of water held by 1 g of PCF.2.2. Preparation of dough and mantouDough and mantou were both prepared with 0e15% PCF by themethod of Wu et al [3]. Unless stated otherwise, the basic 10%fiber-enriched dough constituents were wheat flour (90%), PCF(10%), water (54%), yeast (1.5%), sucrose (8%), shortening (5%),and sodium stearoyl 2-lactylate (0.5%). In brief, all ingredientswere mixed and kneaded to form dough. The dough was thenfermented, sheeted, rolled, divided, proofed, steamed, andcooled. Rheological and quality tests of the dough and mantouwere performed at room temperature (approximately 26C) assoon as possible.2.3. Extension test of unfermented or proofed doughA texture analyzer (TA-XT2i; Stable Micro Systems, Surrey,UK) was equipped with a probe of Kieffer dough and glutenextensibility rig, and operated in tension mode. The pretestand test speeds were both set at 2.0 mm/s to avoid vibrationsthat may occur at high speed. The resistance to the extension(mN) and extensibility (mm) of dough without yeast andproofed dough were determined by recording the maximumforce and the distance at rupture. The measurements wereconducted in six repetitions.2.4. Stress relaxation of mantouThe stress relaxation of mantou was measured according tothe method proposed byWuet al [3]. In brief, the center crumbsample (3 3 4 cm3) was removed by cutting. Stress relaxationtest of the sample was executed by using a texturalanalyzer equipped with a P20 cylindrical probe (20-mmdiameter). The sample was deformed by penetration to aconstant strain of 20% with a test speed of 0.5 mm/s. The dataacquisition rate was 10 points per second. The residual forcewas continuously recorded as a function of time for 480 seconds.The measurements were conducted in triplicate.The stress relaxation data were analyzed by using thePelegeNormand model (Equation 1), proposed by Peleg andNormand [2
การแปล กรุณารอสักครู่..
