## 1 Introduction  
Kiwifruit, known for its tasty, juicy, and sweet-tart flavor, has often been named the \"Vitamin C King\" and \"King of Fruits\", enjoying global popularity [1]. The soluble solid content (SSC) serves as a crucial indicator for assessing kiwifruit quality, influencing taste, acceptability, and market price, and is used to determine its ripeness and optimal harvest time [2]. SSC has been employed in quality assessment and grading to determine the quality level of kiwifruit, impacting pricing and distribution strategies [3]. Therefore, the rapid and non-destructive detection of SSC is vital for guiding harvesting, storage, and processing. Traditional SSC measurement involves extracting fruit juice and determining its refractive index with a refracometer [4]. Although straightforward, this approach is time-consuming, destructive to the samples, and requires significant manual handling. Moreover, the refracometer cannot directly assess solid samples, necessitating juice extraction for each measurement. Additionally, the need to clean the instrument after each use prolongs the process and increases the likelihood of human error. In recent years, non-destructive detection technologies, such as machine vision [5], spectral analysis [6], and electronic nose technology [7], have been widely used in food and agricultural product testing. Machine vision can only reflect the appearance information of the sample and is suitable for coarse grading. The electronic nose system, which uses sensors and algorithms for detection, is expensive and large, limiting its on-site application. Spectral analysis, which can generally collect surface layer (10-20 mm) spectra of samples to obtain chemical composition, offers rapid, accurate, non-destructive, portable, and cost-effective advantages and has been extensively used for agricultural product quality detection [8]. Compared with refracometers, machine vision, spectroscopy, and electronic nose technologies offer distinct advantages for non-destructive testing. Machine vision excels at detecting external appearance, while spectroscopy provides rapid, accurate, and non-invasive measurements of surface spectral information to estimate SSC and other quality parameters. The electronic nose is highly sensitive to volatile compounds, though its high cost and large size limit its field applications. These advanced technologies address the refractometer limitations of being time-consuming, destructive to samples, and labor-intensive. Near-infrared (NIR) spectroscopy enables non-destructive quality assessment by measuring the absorption characteristics of the chemical components within samples [9]. Modern portable spectrometers are lightweight, easy to operate, and feature real-time data transmission and cloud processing capabilities, which can make agricultural testing more efficient and precise, reduce waste, and ensure high-quality fruit for consumers. In recent years, many scholars have conducted extensive research on the quality indicators of kiwifruit, including SSC [10], firmness [11], dry matter [12], titratable acid [13], and starch content [14]. Furthermore, the research on the spectra acquisition conditions of kiwifruit has also deepened, such as the influence of different origins [15], temperatures [16], maturities [17], and storage methods [18]. Additionally, research on data processing algorithms has also progressed, such as various preprocessing methods [19], effective wavelength selection methods [20], and neural network-based analysis techniques [21]. However, research on the effect on spectral acquisition methods of SSC evaluation for kiwifruit has been limited. When NIR light interacts with biological tissue, it can be absorbed, reflected, or transmitted, with its behavior closely related to the chemical composition and physical structure of the samples [22]. NIR spectroscopy can reveal the physical structure and chemical information of the sample, such as the distribution of water, fat, and proteins.