Experimental Study On Bamboo Shoots Drying By Microwave, Hot-air Thin-layer And Their Combined Method

Bamboo shoots contain multi-nutriment, such as protein, fat, starch, meal fibre, calcium, phosphorus, iron, carotene, vitamin B and C etc., and are known as the best green natural food and "The first of vegetable". The plant area of bamboo in china occupys thirty percent of the total area of that all over the world, and is the largest one in the world, but they have obvious regional characteristics. Annual export volume of relational products of bamboo and bamboo shoots reached 800 million U.S. dollars. However, because fresh bamboo shoots only are produced in spring, and easily lignify after harvest, and harvest-time and storage-time are short. The storage of bamboo shoots dried to enrich people's food basket and increase their income is of great significance.To gain dried bamboo shoots of "high quality, high efficiency, low consumption, low emission", the study of bamboo shoots in this paper had adopted research methods of orthogonal experiments, comparison and technology optimization experiments, ensued technology evaluation system of drying bamboo shoots, researched drying characteristics of bamboo shoots, optimal combination conditions of killing blue of bamboo shoots with microwave and best drying technology by hot-air thin-layer and microwave-hot-air thin-layer drying of bamboo shoots, validated drying mathematics models of drying bamboo shoots by hot-air thin-layer. We had analyzed experimental data of experiments in this paper by making use of the software of Excel and DPS.1. Technology evaluation system of drying bamboo shoots of bamboo shoots was established, and gaining comprehensive scores of various experimental results with it. From analyzing the orthogonal experiment data of drying bamboo shoots by hot-air thin-layer drying, the results are as follows:①Drying bamboo shoots by hot-air thin-layer drying with wind speed 3.05m/s and temperature 65℃for the best excellent combination;②Drying bamboo shoots by hot-air thin-layer drying with wind speed 1.58m/s and temperature 65℃for the hypo-excellent combination. But the comprehensive scores of the both combinations are similar by comparing with each other, and the total energy consumption of the best excellent combination is larger. So, drying bamboo shoots by hot-air thin-layer drying with wind speed 1.58m/s and temperature 65℃is deemed to the best craft in the product process.From analyzing the orthogonal experiment data of the microwave-hot-air thin-layer combined drying of bamboo shoots, the results are as follows:①Bamboo shoots had been dried for twenty minutes with 250W microwave power first, then that were dried by the microwave-hot-air thin-layer combined drying with with wind speed 1.58m/s and temperature 65℃for the best excellent combination;②Bamboo shootd had been dried for two minutes with 750W microwave power first, then that were dried by the microwave-hot-air thin-layer combined drying with with wind speed 1.58m/s and temperature 65℃for the hypo-excellent combination. But the comprehensive scores of the both combinations are similar by comparing with each other, and the total time-consuming of the best excellent combination is larger. So, bamboo shoots had been dried for two minutes with 750W microwave power first, then that were dried by the microwave-hot-air thin-layer combined drying with wind speed 1.58m/s and temperature 65℃is deemed to optimal production technology.According to those experiments above, single microwave drying won't normally accomplish the drying of bamboo shoots, and single hot-air thin-layer drying will consume too much energy and time. Compareing with the both drying means above, microwave-hot-air thin-layer combined drying is a very excellent drying mean.2. The experiment results of microwave killing blue and tradition killing blue had indicated:the former outgoed the later, and 900W microwave power, killing blue for 60s for optimum excellent combination in bamboo shoots killing blue with microwave.3. The experiment on comparison temperature drying characteristics of bamboo shoots had indicated:with the same load of bamboo shoots, the temperature higher, the speed of drying swifter; the drying time shorter, curve of lose water rate more unconspicuous in the three drying phases; with the same drying temperament, the load of bamboo shoots larger and drying rate lower, the drying time longer and curve of lose water rate more conspicuous in the three drying phases. The experiments on the characteristics of microwave drying had indicated:the microwave power bigger, the drying time shorter and drying rate higher.4. The results of drying bamboo shoots by several microwave powers, namely,150W,250W, 350W,450W,550W,650W,750W etc. had indicated:bamboo shoots had been dried for some time by those microwave powers mentioned above, the surface of bamboo shoots would come forth some speckles, which influenced the quality of products of bamboo shoots. The color of spackles would become deeper and more, and would lose their market value and the significance of drying at last, if bamboo shoots went on being dried.5. The mathematics models of hot-air thin-layer drying contain single-item diffuse model, exponential model and page equation. The analyzing results of experiment data had indicated: single-item diffuse model MR=Bexp(-At) was the best model for bamboo shoots by hot-air thin-layer drying.6. Comparing the curves of drying time, resume proportion, resume ratio and total energy consumption, the results had indicated:microwave-hot-air thin-layer combined drying outgoed single hot-air thin-layer drying on the drying of bamboo shootd. The former was a bit worse than the later on the quality of bamboo shoots dried, but very similar, which deeply had proved the superiority of microwave-hot-air thin-layer combined drying, and microwace-hot-air thin-layer combined drying would be preferred mean of drying ones of bamboo shoots in the future.