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The purpose of this paper was to explore the utility of an electronic nose to detect the quality of litchi fruit stored in different environments. In this study, a PEN3 electronic nose was adopted to test the storage time and hardness of litchi that were stored in three different types of environment (room temperature, refrigerator and controlled-atmosphere). After acquiring data about the hardness of the sample and from the electronic nose, linear discriminant analysis (LDA), canonical correlation analysis (CCA), BP neural network (BPNN) and BP neural network-partial least squares regression (BPNN-PLSR), were employed for data processing. The experimental results showed that the hardness of litchi fruits stored in all three environments decreased during storage. The litchi stored at room temperature had the fastest rate of decrease in hardness, followed by those stored in a refrigerator environment and under a controlled-atmosphere. LDA has a poor ability to classify the storage time of the three environments in which litchi was stored. BPNN can effectively recognize the storage time of litchi stored in a refrigerator and a controlled-atmosphere environment. However, the BPNN classification of the effect of room temperature storage on litchi was poor. CCA results show a significant correlation between electronic nose data and hardness data under the room temperature, and the correlation is more obvious for those under the refrigerator environment and controlled-atmosphere environment. The BPNN-PLSR can effectively predict the hardness of litchi under refrigerator storage conditions and a controlled-atmosphere environment. However, the BPNN-PLSR prediction of the effect of room temperature storage on litchi and global environment storage on litchi were poor. Thus, this experiment proved that an electronic nose can detect the quality of litchi under refrigeratored storage and a controlled-atmosphere environment. These results provide a useful reference for future studies on nondestructive and intelligent monitoring of fruit quality.

Accurate litchi identification is of great significance for orchard yield estimations. Litchi in natural scenes have large differences in scale and are occluded by leaves, reducing the accuracy of litchi detection models. Adopting traditional horizontal bounding boxes will introduce a large amount of background and overlap with adjacent frames, resulting in a reduced litchi detection accuracy. Therefore, this study innovatively introduces the use of the rotation detection box model to explore its capabilities in scenarios with occlusion and small targets. First, a dataset on litchi rotation detection in natural scenes is constructed. Secondly, three improvement modules based on YOLOv8n are proposed: a transformer module is introduced after the C2f module of the eighth layer of the backbone network, an ECA attention module is added to the neck network to improve the feature extraction of the backbone network, and a 160 × 160 scale detection head is introduced to enhance small target detection. The test results show that, compared to the traditional YOLOv8n model, the proposed model improves the precision rate, the recall rate, and the mAP by 11.7%, 5.4%, and 7.3%, respectively. In addition, four state-of-the-art mainstream detection backbone networks, namely, MobileNetv3-small, MobileNetv3-large, ShuffleNetv2, and GhostNet, are studied for comparison with the performance of the proposed model. The model proposed in this article exhibits a better performance on the litchi dataset, with the precision, recall, and mAP reaching 84.6%, 68.6%, and 79.4%, respectively. This research can provide a reference for litchi yield estimations in complex orchard environments. [ABSTRACT FROM AUTHOR]

The shortage of precooling equipment in litchi-producing regions could lead to a high loss rate and poor quality of litchis. It is urgent to develop a portable precooling device for litchi-producing regions. In this study, a novel spray hydrocooler with thermal energy storage (TES) was designed, fabricated, and tested. A simple mathematical model of TES capacity, the ice-on-coil thermal resistance, and refrigeration system was employed to determine the hydrocooler parameters. Then, the structure of the spray hydrocooler was designed. The maximum charging test was implemented with full TES capacity, and the litchi spray hydrocooling experiments were carried out at different charging times (3–6 h), spray flow rates (30–60 L min−1), and litchi loads (8–28 kg) with one-third TES capacity. Results showed that: (1) the spray hydrocooler allows for the rapid and effective precooling of litchis within 15 min after harvest; (2) the hydrocooler can precool 299 kg litchis with one-third TES storage, meeting the precooling requirements; (3) the effective TES capacity achieved 1.25 × 108 J at the maximum TES capacity of the hydrocooler, while the energy efficiency ratio (EER) is 2; (4) the precooling capacity was maximum and the average power consumption was minimum when the litchi load was 23 kg and the spray flow rate was 30 L min−1. Longer charging time is the most important factor in increasing the precooling capacity and reducing the average power consumption. It provides feasible precooling equipment for rapid precooling in litchi-production regions. [ABSTRACT FROM AUTHOR]

To ensure litchi fruit yield and quality, reasonable blooming period management such as flower thinning is required during the early flowering period. A combination of the number of litchi flowers and their density map can provide a reference for blooming period management decisions during the flowering period. Flowering intensity is currently largely estimated manually by humans observing the trees in the orchard. Although some automatic computer vision systems have been proposed for estimating flowering intensity, their overall performance is inadequate to meet current flower-thinning needs, and these systems are weak in some situations such as in varying environments and when the target object has a low-density distribution. With male litchi flowers as the research object, the goal of this study was to design a method for calculating the number of flowers. By using an image of the male litchi flower as input to a multicolumn convolutional neural network, a final density map and the number of flowers were generated. Experimental results using a self-constructed male litchi flower dataset demonstrated the feasibility of outputting a density map and flower count. The flower number was estimated from the model with a mean absolute error (MAE) that reached 16.29 and a mean square error (MSE) reaching 25.40 on the test set, which was better than counting by target detection. The proposed method can be used to perform time-saving analyses to help estimate yield and implement follow-up orchard management, and it demonstrates the potential of using density maps as outputs for estimating flowering intensity. [ABSTRACT FROM AUTHOR]

• Most damage of fruits was induced before 10 times of impacts. • Damage degree increased with the increase of total impact energy. • Increase of frequency increased the detaching efficiency and reduced the average impact times. • Vibration frequency of 32 Hz induced the lowest average estimated damage degree. Mechanical damage caused by fruit-to-fruit impact is a major challenge for mechanical harvesting of litchi (Litchi chinensis Sonn) fruits. Guiwei litchi fruits were used to study the impact behavior and damage degree due to multiple fruit-to-fruit impacts. The effect of impact times and impact energy absorbed by fruits on fruits damage degree were studied by using a pendulum device. The damage degree of fruits was determined with the modulus of elasticity of fruits. A comb-shaped shaker was used for mechanical detaching tests while the detaching time, impact times and impact energy absorbed of litchi fruits during vibration process at three frequencies of 18 Hz, 25 Hz and 32 Hz were investigated based on a high-speed camera. The results of the pendulum tests showed that the damage degree of litchi fruits increased with the increase of the string length from 0.1 m to 0.35 m at all impact times and most of the damage was caused before 10 times of impacts. Furthermore, the damage degree increased according to a power function (R 2 = 0.9433) with the total impact energy absorbed of all impacts, which can be used to estimate the damage degree of a fruit after multiple impacts. The mechanical detaching tests showed that 90% fruits were detached in 1.2 s, 0.9 s and 0.5 s at 18 Hz, 25 Hz and 32 Hz respectively and the average impact times decreased from 13.1 times to 6.6 times with the increase of frequency. The calculation results showed that a vibration frequency of 32 Hz induced the lowest average estimated damage degree, which was 5.69%. Therefore, harvesting litchi fruits mechanically at high rate and low damage might be feasible with a proper shaking frequency. [ABSTRACT FROM AUTHOR]

Litchi is special fruit in China. It is important and difficult to keep fresh for litchi during transportation after harvest because it matures in hot seasons and will deteriorate rapidly while stored and transported in normal atmospheric temperature. Foam box with ice, refrigeration, and controlled atmosphere are three main fresh-keeping transportation modes for litchi at present. In order to obtain the effects of different fresh-keeping transportation modes on the quality of litchi fruit, the experiments of these three fresh-keeping transportation modes for "Feizixiao" litchi were carried out based on fresh-keeping transportation platform for fruits and vegetables. The developed fresh-keeping transportation platform can adjust temperature, relative humidity and oxygen volume fraction automatically and intelligently according to initial parameters setting and real time feedback from container to create a suitable fresh-keeping environment for litchi. The main processing of the three experiments is conducted as follows. For the experiment of ice-added transportation in foam box, litchi was packaged with polyethylene bags and then put into foam boxes with appropriate crushed ice (mass proportion of ice to fruit was about 0.30) to maintain low temperature. While for the refrigerated transportation experiment, litchi was packaged with perforated polyethylene bags (aperture ratio was 5%) and then put into plastic baskets, keeping the container environment temperature of 3-5°C and relative humidity of 90%-95%. The package type of the controlled atmosphere transportation experiment was the same as that of the refrigerated transportation experiment and the two experiments were at the same temperature and relative humidity in container, but the oxygen volume fraction should be set to 3%-5%. On this basis, the foam boxes or plastic baskets with packaged litchi were fixed on the vibration device workbench located in the container of fresh-keeping transportation platform, and set the vibration acceleration of 0.25 g (gravitational acceleration) corresponding to the vibration level of 70-80 km/h running on highway. The main fresh-keeping quality parameters of litchi were tested per 24 hours, mainly including mass loss rate, good fruit rate, browning index, total soluble solide content, titrable acidity, firmness of pulp, relative conductivity of pericarp and shelf life quality. Results indicated that the effects of three fresh-keeping transportation modes on the quality of litchi within 1 day of transportation time had no significant difference (p>0.05). However, the refrigerated transportation and controlled atmosphere transportation could effectively delay the quality decline of litchi along with the extension of the transportation time. The controlled atmosphere transportation could significantly delay the decline of pulp firmness, total soluble solids content, pericarp relative conductivity and shelf life quality (p<0.05) after 4 days of transportation compared with the other two transportation modes. It could be concluded that the three transportation modes were all suitable for the litchi quality keeping within 1 day of transportation period; and the refrigerated or controlled atmosphere transportation would be better for the litchi transportation lasting for 2-4 days; however, the controlled atmosphere transportation mode would be the most appropriate selection for the litchi transportation for more than 4 days. The research can provide a reference for the selection of fresh-keeping transportation mode for litchi fruit. [ABSTRACT FROM AUTHOR]

Litchi downy blight caused by Peronophythora litchii is the most serious disease in litchi production, storage and transportation. Existing disease identification technology has difficulty identifying litchi downy blight sufficiently early, resulting in economic losses. Thus, the use of diffuse reflectance spectroscopy to identify litchi downy blight at different stages of disease, particularly to achieve the early identification of downy blight, is very important. The diffuse reflectance spectral data of litchi fruits inoculated with P. litchii were collected in the wavelength range of 350–1350 nm. According to the duration of inoculation and expert evaluation, they were divided into four categories: healthy, latent, mild and severe. First, the SG smoothing method and derivation method were used to denoise the spectral curves. Then, the wavelength screening methods competitive adaptive reweighted sampling (CARS) and successive projections algorithm (SPA) were compared to verify that the SPA method was more effective. Eleven characteristic wavelengths were selected, accounting for only 1.1% of the original data. Finally, the characteristic wavelengths were tested by six different classification models, and their accuracy was calculated. Among them, the ANN model performed best, with an accuracy of 90.7%. The results showed that diffuse reflectance spectroscopic technology has potential for identifying litchi downy blight at different stages, providing technical support for the subsequent development of related automatic detection devices. [ABSTRACT FROM AUTHOR]

• A program was developed to analyze the fruit motion in high-speed videos. • Most litchi fruit were detached at quasi-static tilting test without traction. • Stress exceeding ultimate stress was a main detachment reason. • Inducing large tilting angles was advantageous for increasing detachment speed. A high-speed camera was used to study the motions of litchi fruit during vibrational harvesting to investigate fruit detachment patterns. The quasi-static traction and tilting tests, as well as vibrational detachment tests using frequencies of 9, 12 and 15 Hz and amplitudes of 100 and 130 mm, were conducted on 'Huaizhi' litchi. A MATLAB program was developed to estimate the motion parameters of the fruit during shaking. The quasi-static tests indicated that the detachment force decreased as the tilting angle increased from 0° to 60° and that most fruit would detach at a certain tilting angle (average value of 62.6°) without traction. The vibrational detachment tests suggested two main reasons for fruit detachment: the stress exceeded the ultimate stress at the fruit–stem junction and fatigue induced by the alternating stress at the junction. Inducing a large tilting angle during shaking was advantageous for creating a high degree of stress at the fruit–stem junction and for achieving a high detachment speed. In general, appropriate increases in the vibration amplitude and frequency decreased the degree of fruit damage by causing fewer impacts. In this study, 12 Hz/130 mm and 15 Hz/100 mm were the optimal parameter combinations to achieve limited litchi fruit damage and high detachment speeds. [ABSTRACT FROM AUTHOR]

• The end of deformation phase was the most dangerous position during impact. • With the increase of drop height, maximum contact area increased and contact time decreased. • There was a power relationship between impact energy and compressed depth. • There was a linear relationship between compressed volume and damage degree. • Litchi cultivar have influence on damage degree and damage susceptibility. Mechanical damage induced by impact during shaking harvesting or transportation debases the quantity and shortens the shelf life of litchi fruit. In this paper, 'Nuomici' and 'Guiwei' litchis were used to study the impact behavior between fruit and a rigid plate with a new measuring method in order to achieve an approach to evaluate the damage degree and the damage resistance. Impact tests were conducted on a pendulum device and the impact force, compressed depth and contact length were recorded with a force sensor and a high-speed camera. Based on these data, a method was introduced to calculate the contact area, average surface pressure and compressed volume at any given moment of the impact. Analysis of the impact process indicated that the end of deformation phase was the most dangerous moment for a fruit during the impact in all cases. For both cultivars, as the drop height increased from 200 mm to 800 mm, the percentage of absorbed energy, the maximum contact area and the damage degree increased, while the contact time decreased. The maximum surface pressure remained stable as the drop height ranged from 400 mm to 800 mm, so that surface pressure was not a main factor affecting the damage degree. The damage degree of 'Guiwei' and 'Nuomici' were 13.34% and 13.27% at drop height of 200 mm and 27.89% and 23.74% at 800 mm. Respectively, 70% and 79% damage degree happened at drop height of 400 mm. The difference of litchi cultivar has low effect on contact area and contact time, but significant effect on damage degree when drop height was 600 mm and 800 mm. Based on elastic theory, power models with high coefficient of determination were successfully used to fitting the relationship between impact energy and compressed depth for both cultivars. Combined with the good linear fittings between compressed volume and damage degree, the damage degree could then be predicted with impact energy. Furthermore, the damage susceptibility (DS) was introduced to describe the susceptibility of impact damage of litchi fruit. The results show that DS decreased with the increase of drop height. 'Nuomici' was more resist to impact damage than 'Guiwei' as drop height changed from 600 mm to 800 mm. The new method presented in this study can be used to evaluate the damage of litchi fruit and optimize the design of litchi shakers. [ABSTRACT FROM AUTHOR]