榛果發育過程中主要營養成分的變化

摘 要: 以雜種榛優良品系82-11，84-237和84-402為試材，采用動態監測的方法，研究果仁發育過程中營養成分的變化，并分析了營養成分和礦質元素的相關性。結果表明，還原糖的含量前期呈下降趨勢后期略有回升；蔗糖的含量呈上升趨勢，在果仁成熟時成為主要的可溶性總糖；可溶性總糖在果仁發育期呈下降趨勢，從果仁充實期到果仁充分成熟，含量逐漸升高；淀粉的含量呈上升—下降—平穩—上升趨勢；粗脂肪和粗蛋白質的含量逐漸升高，呈明顯累積趨勢。果仁中蔗糖和可溶性總糖的積累主要在果仁發育的后期，粗脂肪和粗蛋白質的積累主要在果仁發育的前期和中期。果仁發育中，粗脂肪含量和氮素，磷素以及鉀素呈極顯著的正相關關系。

關鍵詞: 榛子； 果仁； 營養成分； 積累； 相關性

中圖分類號: Ｓ６６4．4 文獻標志碼: Ａ 文章編號: １００９－９９８０（２０12）０2－0217－０6

Changes in nutrition components in hazelnut during fruit development

ZHAI Qiu-xi，WEI Li-hong

（Liaoning Agricultural College， Xiongyue， Liaoning 115009 China）

Abstract: Three hybrid hazelnut （Corylus heterophylla） lines， 82-11， 84-237 and 84-402， were selected to study changes in nutrition components as well as their correlations with N， P and K. The results showed that the content of reducing sugars decreased in the initial stage and recovered slightly during the late stage. The content of sucrose showed an increasing trend and was the main soluble sugar in maturing kernel. Total soluble sugar content decreased in kernel growth phase and increased gradually from kernel filling phase till full maturity. Starch content increased first and then decreased to and maintained at a low value for a period and increased finally. Crude fat and crude protein contents increased constantly. The accumulation of sucrose and soluble sugars occurred mainly during the late stage of kernel development， while crude fat and crude protein accumulation occurred mainly during the initial and middle stage of kernel development. There existed significant positive correlations between crude fat and N， P and K.

Key words: Hazelnut（Corylus heterophylla）； Kernel； Nutrition； Accumulation； Correlation

Hazelnut（Corylus heterophylla） kernel is nutritious and of high economic value. It is a traditional produce for export and one of the most important nuts in international trade[1]. Hazelnut kernel can be used to extract oil and make candy and cake， and serve as raw materials for medicine， species and dye manufacturing. Up to now， studies related to hazelnut have focused mostly on breeding， quality identification and selection of superior varieties[2-4]. There has been much research about the changes in nutrients during the fruit development in citrus， apricot and kiwifruit[5-7]， while there is little information about hazelnut kernel nutrition dynamics[8-10]. This paper examined changes in the nutritional components in the kernel of three hazelnut crossbred lines throughout fruit development in order to obtain a deep insight into the nutrition accumulation characteristics of the kernel and also the correlations between nutrition components.

1 Materials and Methods

1.1 Materials

Twenty one 7-year-old trees each of 3 hazelnut crossbred lines， i.e. 82-11， 84-237 and 84-402， were selected with a completely randomized design[11] from Fruit Specimen Garden at the Liaoning. Every seven trees were treated as one block with three replicates. The trees were planted at a space of 2 m×3 m， trained as a bundle-like shape. There was some fertilizer application in 2007， since then till the experiment， we have never made any fertilizer application. The soil in which the hazelnut trees were growing contained 12.24 g·kg-1 organic matter， 1.03 g·kg-1 total nitrogen， 42.79 mg·kg-1 available nitrogen， 123.82 mg·kg-1 available phosphorus and 113.48 mg·kg-1 available potassium with a pH value of 5.18.

1.2 Sampling

Samples were collected at 4 to 7 day intervals during kernel development. For each sampling， 50 to 100 fruits were selected randomly from different sections and directions of the tree canopy. Line 1 （82-11）， which matured on August 17， was sampled for six times；Line 2 （84-237）， which matured on August 28， was sampled for eight times， while Line 3 （84-402） matured on September 1 and was sampled for nine times.

The hazelnut kernel development could be divided into four phases: （1） Kernel growth phase， during which kernel volume increased remarkably. （2） Kernel filling phase， when dry matter accumulated in kernel. （3） Nut maturity phase， when nut color changed from white to red or red brown. （4） Nut falling-off phase， during which nuts matured completely and fell off naturally.

1.3 Pretreatment of samples

After sampling， the fruit was placed in an ice bottle， and transferred to the laboratory as soon as possible. After removing the shell， the kernel fresh weight was measured immediately. Kernel was washed with deionized water and enzymes were inactivated in an oven under 90 ℃ for 15 min. After cooling to 65 ℃ for 24 h， the kernel dry weight was measured， and then the sample was ground in a mill and stored for use[12].

1.4 Analytical methods

Reducing sugar was determined using the potassium ferricyanide reduction iodimetry method[13]， and total soluble sugar determined by Shaller-Somogyi’s method[13]. Sucrose content was calculated from reducing sugar and soluble sugar contents. Starch was hydrolyzed directly by acid into glucose， which was then determined by anthrone reagent colorimetry method[14]. Crude fat content was determined using soxhlet extraction method[13]. The content of crude protein was calculated by multiplying conversion factor by nitrogen content， which was determined by the Kjeldahl method[13].

Nutrition content was all expressed in % （g·100 g kernel-1）. The statistical analysis was conducted using the statistical package SPSS18.0. Per kernel nutrition amount=nutrition content × per kernel fresh weight; per kernel nutrition net increase =per kernel nutrition amount differentials between two adjacent samplings; nutrition increase rate =per kernel net increase/per kernel nutrition amount at full maturity[15].

2 Results and Analysis

2.1 Sugar content dynamics in kernel during hazelnut development

Reducing sugars and soluble sugars demonstrated different change patterns during hazelnut kernel development （Fig.1 and 2）. There existed a rapid decrease in reducing sugar during kernel growth phase from August 5 to August 12 in all the three crossbred lines. From August 12 to full maturity， reducing sugars showed a recovering trend （Fig. 1）.

Sucrose content increased with kernel development. The increase was slower during the growth phase， while from kernel filling phase to nut maturity phase， sucrose content in the kernel increased remarkably in all the three lines. 82-11 was an early ripening variety， and the sucrose content at full maturity was 3.35%. 84-237 was a mid-late ripening variety， and sucrose content reached up to 3.77%. 84-402 was a late ripening variety with a sucrose content of 4.12%. When fully matured， the percentage of sucrose against total soluble sugars was 89.05%， 79.02% and 79.09% in 82-11， 84-237 and 84-402， respectively. A previous study showed that that during apple initial development period， there was almost no sucrose accumulation， and fructose content was relatively low， while glucose content was comparatively high. However， during late development period， there was a substantial accumulation of sucrose[16].

Changing pattern of total soluble sugars is displayed in Fig. 3. Soluble sugar content showed a decreasing trend during kernel growth phase from 1.94% to 1.49% in 82-11， from 2.37% to 1.04% in 84-237， and from 2.20% to 0.83% in 84-402. From kernel filling period till full maturity， soluble sugar content increased continually and reached 3.77%， 4.77% and 5.22% in 82-11，84-237 and 84-402， respectively.

2.2 Changes in starch， crude fat and crude protein contents during hazelnut kernel development

Starch， crude fat and crude protein results are shown in Table 2. Based on DMRT significance test， there were significantly positive correlations of starch， fat and protein contents with sampling date within the same line. With the development of kernel， starch content first increased， then decreased to and maintained low levels for a period and finally increased again. Starch accumulation occurred primarily during kernel filling and maturation phases， and at full maturity starch content in 82-11，84-237 and 84-402 was 5.53%， 8.68% and 6.63%， respectively. Fat content increased substantially from kernel growth phase till kernel maturity phase. Upon full maturity， fat content increased to 54.54%， 56.74% and 46.86% in 82-11， 84-237 and 84-402， respectively. There was an obvious increasing tendency in fat content on fresh weight basis and also on dry weight basis. Crude protein content increased with the filling of the kernel. During this period， kernel developed quickly， filling the seed cavity with rapid increase in dry matter content[17]， and there was high nitrogen accumulation till fruit matured and fell. When kernel fully ripened， crude protein content amounted to 16.57%， 13.21% and 15.88% in 82-11， 84-237 and 84-402 respectively.

2.3 Changes in kernel nutrition increase rates during hazelnut development

Net nutrition increase rate was calculated to give a clear picture of nutrition accumulation pattern during hazelnut kernel development （Table 3）. By August 5， sucrose had accumulated to 48.79% and 24.74% of the final sucrose content at full maturity in 82-11 and 84-237， respectively. It reached 77.86% and 92.39% respectively on August 12. While in 84-402， it was 48.81% on August 17 and reached 90.42% on August 28. The results suggest that the accumulation of sucrose occurred mainly during the late stage of kernel development. Soluble sugar accumulation occurred primarily during late stage of kernel development as well. On August 12， total soluble sugars increased to 78.99% and 81.48% of the final value in 82-11 and 84-237， and on August 21 it was 65.63% in 84-402.

From July 30 to August 5， crude fat accumulation rose from 44.39% to 77.30% in 82-11 and from 28.79% to 61.45% in 84-237. For 84-402， crude fat accumulation value was 32.88% on August 5 and increased to 65.87% on August 12. The above results indicated that the fat accumulation in kernel in the three lines occurred mainly during the early and middle kernel development stages， when reducing sugar and starch contents reduced constantly， indicating conversion of carbohydrates into to fat. During the late development stage， fat content continued to increase， but with a smaller accumulation value， 22.70%，38.55% and 34.13% in 82-11，84-237 and 84-402， respectively. Crude protein accumulation on July 30 reached 71.53% and 73.06% in 82-11 and 84-237， respectively. And in 84-402 it reached 70.89% on August 12. The results showed that protein accumulation took place chiefly during the early and middle kernel development stages.

2.4 Correlations between crude fat and N， P and K

Correlations between crude fat and N， P and K in the three hazelnut lines are displayed in Table 4. In all the three lines， fat and N， P and K had significant positive correlations with a correlation coefficient ranging from 0.856 to 0.993. The result indicated that during hazelnut kernel development， the enrichment N， P and K content might promote fat accumulation. Changes in distribution and transformation of phosphorus is closely associated with plant metabolism processes and shift in growth center[18-19]. Different from nitrogen and phosphorus， potassium is not a component of any organic matter， nevertheless it was an essential element in the life activities of fruit tree[20-21]. Appropriate amount potassium could accelerate fruit expansion and maturity and potassium accumulation pattern was in agreement with the nutrition requirement during hazelnut kernel development[17].

3 Discussions

Deng et al[22] studied changes in sugar content during peach fruit development and found that reducing sugar content was comparatively high in the initial stage， reduced substantially during rapid fruit growth stage and recovered slightly thereafter with the slackening fruit growth. Jin[23] also found that in the initial stage fructose and glucose were the principle sugars in peach， accounting for 90% of soluble sugars. However in the late stage sucrose content increased markedly and amounted to 80% of soluble sugars when completely ripe.

As a temporary storage form of carbohydrate during hazelnut fruit development， starch plays an important role in accelerating transportation， unloading and metabolism of photosynthetic assimilates from leaves to fruit[24]. There is much emphasis on the crude fat and fat acids of hazelnut kernel[25-27].

Analyses on macadamia demonstrated that during oil accumulation period nitrogen content in leaves declined and that there was abundant demand for nitrogen for oil accumulation[28]. Relevant studies demonstrated that there was close connections between fat， phosphorus and potassium during walnuts kernel filling stage[29]. Fat is transformed from sugars， while synthesis of sugars needs participation of phosphorus and transformation of sugars to glycerol and acid fat also needs phosphorus. Thus it is obvious that phosphorus is a crucial element for fat synthesis[30-33].

During kernel growth period， kernel weight ascended continually. This is also a period of embryo development with accumulation of kernel stored substance such as crude proteins and crude fat， which is an important period to determine kernel yield， nutrition and flavor. Topdressing during the early July and middle July is necessary for fruit retention as well as for fruit development， flower bud differentiation and branch enrichment. For topdressing， N-P-K compound fertilizer is the optimum， and the amount nitrogen fertilizer applied should be well controlled to avoid excessive vegetative growth which reduces yield. Foliar fertilizers， such as 0.3% to 0.5% carbamide or potassium dihydrogen phosphate in combination with microelements and plant growth regulators， applied based on the requirement of tree growth and development are more effective. Additional application from the middle August to early September replenishes the early nutrition consumption， guarantees plant nutrition demanded by fruit ripening， and prevents nutrition deficiency and vigor decline.

4 Conclusions

During kernel development， reducing sugar content was relatively high when kernel growth was fast and low when kernel growth was slow， and reached a bottom value at full maturity. In contrast， sucrose content showed a completely opposite pattern， where it was relatively low at fast kernel growth and high at slow kernel growth and reached a highest value at full maturity accounting for 80% of total soluble sugars. In ripe kernel， sugar accumulation was chiefly due to the accumulation of sucrose.

Sucrose， soluble sugars and starch accumulated principally in the late kernel development stage. For crude fat and crude proteins， the accumulation occurred basically during the early and middle stages. Crude fat showed significant positive correlations with nitrogen， phosphorus and potassium.

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