Hello , it means "mainly", or "made 90% by something". We can say: 这次考试以选择题为主。(90% are...) 在伦敦，人们以说英语为主。(mainly)

Your sentence about Korean food is correct. When we say "A以B为主", it means B is the major part/feature of A, or A is mainly B. B can be a noun or an adjective.

1. An ounce of prevention is worth a pound of cure. 防病为主,治疗为辅. 来自互联网 2. Applies to non - color, color of quadrochromatic. 适用于 非 彩色为主, 彩色为辅的原稿. 来自互联网 3. Spikenonwovenfactory to supplement the mainhardwareproductionpatternfrom the mid - 1980shasnowcome. 本厂以无纺刺针为主五金为辅的生产格局,从八十年代 中期 一直走到现在. 来自互联网 4. Twoalternativeapproaches to classic ASIC - centered and DSP - assisted architectures have emergedandandaccelerator - assistedarchitectures. 于是,出现了两种可供选择的办法:用传统的ASIC为主DSP为辅的结构替换上述结构. 来自互联网 5. The menu is based on classic French cooking. 菜单是以经典的法国菜为主。 来自柯林斯例句 6. Some spirituals are based on syncopated rhythms. 有一些圣歌以切分节奏为主旋律。 来自柯林斯例句 7. The spacious main bedroom is mainly blue. 宽敞的主卧室以蓝色为主色调。 来自柯林斯例句 8. a colour scheme in which red predominates 以红色为主的色彩组合 来自《权威词典》 9. Thecontestbecomesmainlyone of feint and counterfeint. 这场比赛变成了一场以佯攻与反佯攻为主的较量. 来自《简明英汉词典》 10. Stress shouldbeput on the prevention of diseases. 疾病应以预防为主.